A price on a large marketplace is constructed backward from a stack of fees. Understanding that stack explains odd pricing, sudden delistings and unusual pack sizes.
Referral fees come off every sale
The marketplace takes a percentage of the total sale price, with the rate varying by category, applied to shipping revenue as well as to the item.
Because the fee is proportional, raising a price does not improve margin as much as it appears, and lowering one erodes margin faster than it appears.
Categories with lower referral rates attract sellers with thin margins, which is one reason competition varies so much between product types.
Fulfillment charges depend on size and weight
Where the marketplace handles storage and shipping, fees are calculated from dimensional bands, and crossing a band boundary raises the cost in a step.
That step function is why products are redesigned to fit within a band, and why packaging shrinks in ways that seem disproportionate to the contents.
Storage fees accumulate monthly and rise sharply for inventory held a long time, which pushes sellers to discount aging stock rather than hold it.
Advertising has become a required cost
Sponsored placements determine visibility for many search terms, so a seller who does not advertise may not be seen regardless of price or reviews.
That converts advertising from an optional growth expense into a cost of doing business, and it is priced into the item like any other input.
The auction structure means the cost rises with competition, so crowded categories carry higher advertising cost per unit sold than sparse ones.
Returns are charged back to the seller
Returned items generate processing fees and often cannot be resold as new, so a category with a high return rate carries a higher effective cost per sale.
Apparel and footwear are the clearest examples, and their pricing reflects an expectation that a meaningful share of units will come back.
Sellers manage this with sizing information and detailed images, since prevention costs less than processing.
The stack explains multipack pricing
Because several fees are per-unit rather than proportional, selling three items in one shipment costs far less than shipping three separately.
That is why multipacks are often priced below three times the single unit while remaining more profitable for the seller.
It also explains why very inexpensive items disappear from marketplaces entirely, since the fixed portion of the fee stack exceeds what such items can support.