People often go to extreme lengths to fake art, so due diligence becomes tough, full of effort, not to mention trust on both sides that the person is selling something real and that the person buying is going to send it back if they deem it unworthy of purchase.. even the exchanging addresses part or meeting in person is a huge risk.. plus the fact that 90+% of the potential buyers would be law enforcement looking to put you in prison.. the patrons would also have to trust that the whole thing isn't run by the authorities in the first place.. and i'm sure there are a slew of other issues that make this just totally unfeasible.
As long as a way of transferring goods and payments can be agreed on I guess most thieves wouldn't care who their customers are?