It might be worth thinking about some kind of rating system or method for confirming purchases a la Reddit marketplaces. Maybe buyers can create a gopher-accessible file with purchase details and sellers can link to that as a way of building a reputation.
Yes, 100%.
One of the challenges will be getting order information from the buyer to the seller in a way that is consistent and error-free. Item numbers, unit prices, shipping, tax, total due. Without a shopping cart application, sellers might be best served by bundling shipping and tax into the item price. Alternatively, gopher commerce could make use of a purchase order/invoice pattern. That’s a bit more work for everyone, but should reduce miscommunication.