I considered this. I figure ZOS knows more about preventing this sort of exploit than I do. Hmm...but let's brainstorm. Let's assume a crown price of 5000. Random number...but it's what assistants cost, so let's use that.
If you allow one ring active on an account, then to activate another you have to destroy the first, this would probably prevent most exploits. Why spend $50 to transfer items just one time? The one ring rule is also important because A.) the hobbit, duh, and B.) if players had multiple rings then guilds would just establish networks of rings to trade stuff. So for sure you can only have one ring active.
But you'd still have the jerk that farms a pile, charges someone a fortune via PayPal, sets up the ring, transfers items, then destroys the ring to move on to the next. Yeah...I'm sure there are people out there who would spend 5,000 crowns on the ring then send the exploiter like $500 real world dollars. So to prevent this...what sort of safe guards? Maybe you can only activate one ring ever per account? One per year? I think they could demotivate scammers with an appropriate system.
And they'd have to consider how big a problem this would be anyway. A lot of powerful gear is bind on equip. If people weren't running scams for agility jewelry last year or briar heart weapons, I'm not sure how much more of a problem monster masks, trial equipment, etc poses.