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.
They will need to sell something to get positive feedback, so how will they be able to get that feedback if they cannot sell without it?
I Think using escrow would give the buyer unfair privileges over the seller. In my decades of experience buying and selling on the internet it is usually the buyers that tend to be the more problematic users of online marketplaces.
Using escrows protects both parties who can be malicious in their own way. Sellers can try to sell sub standard products and buyers can be too demanding on what they expect.
The way your suggestion can work is if you have all sellers registered and the buyers have a return policy if they do not get the product in the quality that was advertised.
You will be acting as the escrow in that case.
- Jay -