Sellers on Etsy, eBay, Amazon and most third-party marketplaces pay for chargebacks, even though the marketplace owns the customer relationship. When a dispute is filed, the seller holds only part of the order record. The marketplace keeps the messaging, the address and the payment flow. The marketplace also runs the dispute screen and sets its own response deadline, which can fall before the card brand's deadline. The seller cannot see what evidence the marketplace sends for them.
Marketplaces sell buyers on dispute protection. The seller pays for it, because sellers must accept the terms to keep selling.
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For a seller with meaningful marketplace volume, chargebacks in that channel run higher than on the seller's own checkout, and replies to the dispute win less often. Both costs belong in your unit economics. Discount marketplace revenue by the chargeback overhead. The orders worth taking on a marketplace differ from the ones worth taking on your own site.