3) There is probably a wide margin of concern for scamming, since there is not a two way trade of in-game items happening here. I understand this concern. In order to confront that, there could be a few things put in place that might prevent/deter scammers:
-> Have the art-shops who do accept trades in exchange for their work more closely monitored.
-> Only allow an artist to accept trades for their work after their shop has had that clearance from a mod. (could be shown under their signature or name as some type of ribbon or medal) The artist must be able to prove that in the past, they have completed a great deal of requests and completed them on time, and in a professional manner.
-> Customers who get scammed should take the initiate to report the artist and their shop who scammed them. Artists should take it upon themselves to watermark their work until the trade is completed, so as to protect them from being scammed from the other end.