Usually some sort of price discrimination. Let's say Brand X pays $5 to produce something and sells it wholesale for $15 to stores, for a retail price of $30. A

Usually some sort of price discrimination. Let's say Brand X pays $5 to produce something and sells it wholesale for $15 to stores, for a retail price of $30. Assume Amazon fees selling at $30 are $10, so Brand X can sell on Amazon at $30 and get back $20. A third party could divert goods from a retail store, say they pay an extra $1, and price at $28, and will net $18 from Amazon and be left with a profit of $2. Alternatively, maybe a store had overstock and sold the goods in bulk at a loss. Or sometimes they sell the same products cheaper in another country, and it turns out to be cheaper to buy there and import to resell here.