A marketplace supplies demand a seller could not reach alone. What it withholds is the relationship with the buyer, and that omission shapes everything the seller can build.
The platform owns the demand and lends it out
Buyers arrive because they trust the marketplace, search on it and pay through it. The seller is a fulfilment option presented inside someone else's shopping process.
That is a genuine service and it is priced accordingly through commission, advertising and fulfilment fees, which together take a substantial share of the transaction.
The arrangement works well as a channel and poorly as a foundation, because the asset generating the sales is not one the seller is accumulating.
Customer data stays with the intermediary
Sellers typically receive what is needed to ship an order and little else. There is no durable ability to contact the buyer, segment them or market to them later.
Repeat purchase, which is the cheapest revenue available to any retailer, therefore has to be re-bought through the platform each time.
A business whose customers are all held by someone else has no direct channel to activate when it needs volume, which removes its main lever in a difficult quarter.
The rules can change and the seller cannot appeal effectively
Fee structures, ranking behaviour, category policies and enforcement standards are set unilaterally and applied to every seller simultaneously.
A seller whose economics depend on the current settings is exposed to changes that may be entirely reasonable from the platform's perspective and fatal from theirs.
Account suspensions carry the same asymmetry, since the process is designed for scale rather than for adjudicating individual cases quickly.
Competition happens on the same page
Marketplaces place alternatives directly alongside the listing, so differentiation is compressed into price, delivery speed and review count.
Brand attributes that would separate the product elsewhere are largely invisible in that format, which pushes competition toward the dimension with the least margin in it.
Sellers with a genuinely differentiated product often find the channel systematically undervalues the difference they have invested in creating.
The workable position treats the platform as acquisition
Sellers who last generally use marketplaces to reach buyers who would not otherwise find them, then work to move the relationship somewhere they control.
Packaging inserts, warranty registration and follow-on offers are the usual routes, and platform rules constrain each of them, so the transfer is partial at best.
Even a partial transfer changes the business, because a modest owned audience provides pricing latitude and a fallback the pure marketplace seller does not have.