Product research mistakes are the most expensive kind of mistake in Amazon FBA. Buy the wrong product and you are stuck with stock that either sits costing you storage fees or sells at a loss. Here are the patterns we see most often — and how to avoid them.
Ignoring the Fee Breakdown
The most basic mistake is not calculating Amazon's fees properly. A product selling for £20 looks great when you can buy it for £8 — until you realise Amazon takes £3 in referral fees and £2.50 in fulfilment fees, plus £1 for prep and inbound shipping. Your £12 "margin" is actually £5.50. Still decent, but a very different proposition.
Always use the FBA Revenue Calculator before buying. Every single time. No exceptions.
Using Today's Price Instead of Historical Data
Checking only today's Amazon price is like checking the weather right now and assuming it will stay the same forever. Prices fluctuate. A product might be at £25 today because it is temporarily out of stock from other sellers, but its normal price is £15. If you buy stock expecting to sell at £25, you will be disappointed when the price drops back.
Always check at least 90 days of price history using Keepa. The average price over that period is a much safer number to base your calculations on.
Ignoring Seasonal Patterns
Some products sell well at certain times of year and barely move at others. A garden product might have fantastic sales in May but sit dead in November. A Christmas-themed item might look brilliant in October but become unsellable by January — leaving you with long-term storage fees.
Check the sales rank history over a full 12-month period where possible. If demand is clearly seasonal, plan your purchasing and pricing accordingly.
Not Checking the Competition
A product can look profitable based on price and demand, but if there are 20 FBA sellers all competing for the Buy Box, your share of sales will be small and price pressure will be intense. Equally, if Amazon itself is selling the product, competing as a third-party seller is very difficult.
Check the number of FBA sellers on the listing. Fewer than five is ideal. Also check whether the seller count has been increasing — a rising number of sellers often signals that margins are about to be compressed.
Buying Too Much of an Untested Product
Enthusiasm is dangerous in product research. You find a product that looks perfect — great margins, strong demand, low competition — and immediately buy 100 units. Then it does not sell as expected, or the price drops, or a quality issue emerges.
Start with small quantities. Buy 5–10 units to test the market. If they sell as expected, buy more. This limits your downside while you validate your research.
Overlooking Category Restrictions
Some Amazon categories require approval before you can sell in them. Buying stock in a restricted category you do not have access to is a frustrating and surprisingly common mistake. Check whether you can list the product before buying it — not after.
Forgetting About Prep Requirements
Some products need extra prep work — poly bagging, bubble wrapping, "sold as set" stickers, or suffocation warning labels. These add to your per-unit cost and need to be included in your profitability calculation. A product that looks marginally profitable before prep costs might not be worth the effort once they are factored in.
Chasing Trends Too Late
By the time a product trend is widely known, dozens of sellers have already jumped on it. Late entrants compete on price, margins shrink, and the trend fades — leaving latecomers with unsold stock. If you want to capitalise on trends, you need to spot them early, not follow the crowd.
The Discipline of Research
Good product research is disciplined, not exciting. It means saying no to most products and only buying when the numbers genuinely work. The sellers who build sustainable Amazon businesses are the ones who resist impulse purchases and trust their data over their gut feeling.