I’d like to believe it wouldn’t be hard to flag accounts that suddenly become active after years of doing absolutely nothing, then out of nowhere buy premium and try to sell off their limiteds. The whole thing is super obvious and based on patterns that are pretty easy to catch. Stuff like this should immediately throw up red flags, and your system should be able to step in, block further actions on the account, maybe even lock it due to suspicious behavior, and require some kind of verification.
Most of these accounts don’t even have a connected email or any real contact info, and the original owner has probably long lost hope of ever getting back in, or just has no way to do so. So locking down the account and forcing proper verification would honestly be one of the best moves you could make. It pretty much stops whatever the bad actor was trying to do right there.
Once the account’s secure, any potential damage or side effects are basically avoided too. I don’t even think the problem is them selling limiteds — that actually helps put more copies into circulation, which supports the trading economy in the long run. But for obvious account fraud or weird behavior showing up on super old accounts, I really doubt anyone would complain if some action was finally taken.