The problem is not one way, though.
Have you thought about sellers who are scammers and sell fake items to buyers? Now if the seller is going to receive instant payment minus the buyer verifying if what they have received is legitimate, and it turns out to be the opposite, how are you going to solve such disputes minus and active escrow service?
Yes I have thought about bad sellers. The marketplace operator would have to first allow the marketplace user seller privileges before they would be able to sell. There could be some rules set in place such as the user must have a certain amount of positive feedback before they would be able to sell. The disputes would be over seen by the marketplace operator through a feedback system and bad actors would have their marketplace account cancelled.
I was one of the original international sellers on both Ebay and Amazon in the 1990s. This was before electronic internet payment systems such as Paypal even existed and buyers had to snail mail the sellers the payment for the item. I think using similar practices that Ebay had set in place when first launching their online marketplace could successfully be used again to launch community blockchain marketplaces.