There’s a number that determines 80-90% of sales on any competitive marketplace, and most brands and sellers don’t keep it in mind clearly enough: the Buy Box.
On MercadoLibre, it’s the seller who appears in the main position when a consumer lands on a product listing with multiple offers. On Amazon, it’s the yellow “Add to Cart” button, linked to a specific seller among all those competing for that ASIN. The seller who has the Buy Box captures the sale. The one who doesn’t, waits.
I’m not exaggerating when I say that winning or losing the Buy Box can be the difference between a profitable marketplace operation and one that’s just burning advertising budget to drive traffic to sales captured by someone else.
In this article I explain exactly how the Buy Box algorithm works on the two most important platforms in LATAM, what factors control your position, and how to build a systematic strategy to win it and keep it.
What the Buy Box is and why it matters so much
When multiple sellers offer the same product (same ASIN on Amazon, or competing on the same listing on MercadoLibre), the marketplace needs to decide who gets shown the main purchase button to the consumer. That position is the Buy Box.
The impact in numbers:
On Amazon, 82% of sales happen through the Buy Box according to Jungle Scout data. Sellers who don’t have it compete for the remaining 18%, which buyers have to actively seek out by clicking “See all buying options.” On MercadoLibre, the phenomenon is similar, though with less public documentation.
For brands that sell through distributors or that have multiple sellers of the same product, the Buy Box problem is especially acute: if a distributor with lower prices (even marginally) or better reputation wins the Buy Box, the brand loses control over how its product is sold and at what price.
For brands that sell directly (first-party or third-party), winning the Buy Box is an almost necessary condition for advertising investment to be efficient: there’s no point paying for Mercado Ads or Amazon Ads if the traffic you generate ends up converting for another seller who holds the Buy Box.
How the Buy Box algorithm works on MercadoLibre
MercadoLibre doesn’t officially publish its Buy Box algorithm, but through data analysis and operating experience with hundreds of accounts, we can identify the factors that carry the most weight:
Factor 1: Seller reputation (the most important one)
Reputation on MercadoLibre is measured through its thermometer system (green, yellow, orange, red), which is a synthesis of several indicators:
- Claims rate: The percentage of transactions that ended in a formal claim. MercadoLibre heavily penalizes any value above 1%.
- Cancellation rate: Cancellations initiated by the seller (out of stock, pricing error, etc.). The critical threshold is around 3%.
- Shipping delays: Percentage of orders where dispatch happened outside the committed time.
A seller with a red thermometer basically doesn’t compete for the Buy Box, regardless of price. A seller with a green thermometer has a structural advantage.
Factor 2: Total price (price + shipping)
The price the algorithm compares isn’t the product price but the total price the consumer pays: product + shipping cost. A seller with a lower product price but paid shipping can lose against one with a slightly higher price but free shipping.
This is where understanding the value of free shipping on MercadoLibre matters. Listings with free shipping have a visual badge that improves CTR and, crucially, the algorithm favors them in the total-price comparison.
Factor 3: Use of Mercado Envíos and MercadoFull
Listings that use Mercado Envíos (MercadoLibre’s own logistics network) have access to faster and more predictable delivery times, which improves the buyer experience and reduces delay claims. MercadoFull (the fulfillment service where MercadoLibre stores and ships the product) goes a step further: it practically guarantees the platform’s fastest delivery times and has a documented positive impact on ranking.
Factor 4: Sales history on that listing
MercadoLibre favors listings with a sales history and positive reviews. A new listing, even with a low price and a seller with good reputation, can take weeks to establish position against an established one.
Factor 5: Listing quality
Optimized title, complete description, filled-in attributes, quality images. MercadoLibre’s algorithm is increasingly incorporating content quality as a ranking factor.
How the Buy Box algorithm works on Amazon
Amazon is more transparent than MercadoLibre about the factors that determine the Buy Box, although it doesn’t publish the exact weight of each variable.
Factor 1: Basic eligibility
Before competing for the Buy Box, a seller must meet certain minimums: an active account in good standing, and no account metrics in critical status (ODR - Order Defect Rate below 1%, cancellation rate below 2.5%, late shipment rate below 4%).
Factor 2: Competitive pricing
Amazon compares the seller’s price not only against other sellers on the same platform, but also against prices on other sites. If it detects that your price on Amazon is materially higher than in your own store or other channels, it can suppress your Buy Box. This is what Amazon calls “price parity” and it’s one of the most important and least known rules.
The price Amazon compares is the “landed price”: product price + shipping. If you offer Prime shipping (free for members), your product price has to be competitive against the landed price of other sellers with paid shipping.
Factor 3: Fulfillment method
This is the factor with the biggest impact on the Buy Box after price. Sellers with FBA (Fulfillment by Amazon) have a very significant structural advantage over FBM (Fulfilled by Merchant) sellers, even at similar prices. The reasons are faster and more reliable delivery promises, Prime integration, and lower risk of late shipment.
An FBM seller with a price 5-8% lower can still lose the Buy Box to an FBA competitor. The gap you need to win as FBM vs. FBA is often larger than sellers initially calculate.
Factor 4: Seller Feedback Score
The percentage of positive feedback over the last 30 days, 90 days and 12 months. Amazon looks for sellers with more than 95% positive feedback. Below 90%, the chances of winning the Buy Box drop significantly.
Factor 5: Message response time
Amazon measures the response rate within 24 hours to buyer messages. A high non-response rate (more than 10% unanswered within 24h) negatively impacts account metrics and, with them, the chance of winning the Buy Box.
Pricing strategy to win the Buy Box without destroying margin
The most common mistake brands and sellers make when trying to win the Buy Box is entering a thoughtless price war that ends up eroding margin across the entire category. Here’s the right strategy:
1. Define your price floor precisely
Before any pricing strategy, precisely calculate the minimum price at which you can sell without losing money. That calculation should include: product cost + shipping cost (or FBA/MercadoFull) + marketplace fee + estimated advertising cost + expected returns cost + operating cost. That’s your floor. You cannot go below that number, regardless of what the competition does.
2. Monitor competitor prices in real time
Tools like Nubimetrics (for MercadoLibre) or Jungle Scout and Keepa (for Amazon) give you visibility into your competitors’ price movements. Without this visibility, you’re making pricing decisions blind.
3. Implement repricing with smart rules, not just “lowest price”
The mistake many sellers make with automated repricing tools is configuring them in “always the lowest price” mode. That guarantees the Buy Box but also guarantees margin erosion. A smart configuration includes:
- If I’m the only active seller on this listing, keep the price near the ceiling (I don’t need to lower it to win the Buy Box if there’s no competitor).
- If there are competitors but my reputation is significantly better, try to win the Buy Box with a small price advantage (2-5%), not the maximum one.
- If the competitor is selling below my floor, don’t follow them. Report if there’s evidence of predatory pricing or unauthorized product sales.
4. Treat price as a tactical lever, not just an operational one
Calendar events (Hot Sale, Buen Fin, Christmas, Mother’s Day) create windows where an aggressive pricing strategy can capture the Buy Box and build a sales history that later defends the position during normal periods. Planning these windows in advance with a specific budget is an effective strategy.
The role of fulfillment in the Buy Box battle
If there’s a single decision with the biggest individual impact on your ability to win and keep the Buy Box, it’s the fulfillment decision.
MercadoFull vs. self-managed shipping on MercadoLibre:
MercadoFull (MercadoLibre’s fulfillment service) has a proven impact on ranking and Buy Box win rate. Products in MercadoFull get:
- A “Arrives tomorrow” or “Arrives today” badge in many cases, which significantly increases CTR.
- More predictable delivery times, which reduces delay claims.
- Benefits in MercadoLibre’s ranking algorithm.
The cost of MercadoFull (storage + picking + packing + shipping) vs. self-managed logistics depends on volume and product type, but for most medium-to-high-volume categories, MercadoFull is competitive on total cost and superior in marketplace impact.
FBA vs. FBM on Amazon:
FBA’s advantage over FBM in terms of the Buy Box is structural and well documented. Sellers who migrate to FBA typically see a Buy Box win rate improvement of between 15% and 30% for the same ASINs, even without price changes. The additional cost of FBA (storage, picking, shipping) is generally offset by higher sales volume.
Special cases: when unauthorized distributors compete
One of the most frustrating problems for brands selling on marketplaces is when unauthorized distributors (or worse, gray-market products) compete on the same listing with lower prices, winning the Buy Box and selling the product without the brand’s quality control or after-sales service.
To manage this problem:
1. Authorized distributor program: Explicitly establish which distributors are authorized to sell your product on marketplaces and under what conditions (minimum sale price, content and service obligations). This program requires clear contracts.
2. MAP (Minimum Advertised Price): A minimum sale price policy that all authorized distributors must respect. In LATAM it has weaker enforcement than in more mature markets, but it establishes the legal framework to act against violators.
3. Continuous monitoring: Use tools to detect unauthorized sellers on your listings and act quickly: report to MercadoLibre or Amazon, contact the seller directly if identified, and in cases of brand infringement or counterfeit products, follow each platform’s intellectual property complaint process.
4. Control of the master listing: On Amazon, the brand with access to Brand Registry controls the listing’s content (title, images, description) regardless of who’s winning the Buy Box. This is partial protection: even if you don’t control the sale, you do control how your product is presented.
A metrics dashboard to monitor your Buy Box position
A professional marketplace team should systematically monitor these metrics (ideally in a dashboard updated daily):
Buy Box metrics:
- Buy Box win rate: % of time you hold the Buy Box on each ASIN/listing
- Number of active competitors per ASIN
- Your price differential vs. the main competitor
Account metrics (both platforms):
- Order Defect Rate / claims rate
- Cancellation rate
- Late shipment rate
- Customer feedback score
Business metrics:
- Revenue by channel
- Contribution margin per ASIN (net of fee + logistics + advertising)
- ACOS (Advertising Cost of Sale) for sponsored products campaigns
Conclusion: the Buy Box is an asset you build, not just win
The Buy Box isn’t a button you press. It’s the result of multiple correct operational decisions executed consistently over weeks and months: competitive but sustainable pricing, reliable fulfillment, impeccable seller reputation, quality content, fast customer response.
Brands that consistently win the Buy Box and keep it aren’t the most aggressive on price. They’re the ones with the most professional operation. Price, logistics, reputation and content work as a system. When one component fails, the others can’t fully compensate.
The good news is that the factors that determine the Buy Box are, for the most part, under your control. You don’t need an unlimited budget or a structural price advantage. You need a team that understands the rules of the game and an operation that executes them consistently.
What Buy Box factor is costing you the most in your operation today? Is it pricing, reputation, fulfillment? Tell us in the comments — we’re very interested in understanding the specific challenges of different categories and markets. If you want to run a diagnosis of your current Buy Box position and build an action plan, we’re available to help.
By Matías Poso, CEO at Balloon Group a Fastforward AI Company.