Are you able to add a section where people can request items or post a wanted ad? I think it would be a good idea as people might not have an item on hand but they could get it and send it to the buyer. So the seller would confirm the sale and the buyer would have to fund an address before the item is sent. It would be hard to determine scams here though because the buyer wouldn't be able to choose who they're buying from. If you feel like adding this it would be a good idea to have options where the buyer can limit the requirements of the seller (10+ Feedback, No negative, No unpaid items, etc.).