Not sure I understand the facts entirely, but assuming this is online gaming and not gambling, buying the accounts likely violates the Terms of Service of the respective accounts. A lawsuit might be possible but likely not worth it unless you are out a significant amount of money.
This is not legal advice but a general comment on society.
It's hard to give a reliable answer from the factual description you have posted, but it sounds like there may be a breach of contract claim at issue (and potentially other claims). However, just because you have a potential claim, doesn't make it a wise decision to file a lawsuit. Lawsuits can (and usually do) get very expensive very fast. If you want to pursue any potential claim, the first thing you should do is consult with an experienced attorney so that they can provide advice based on a full understanding of the facts.
I am an attorney, but I am not YOUR attorney. By providing free, generalized information, I am not entering into an attorney/client relationship with you, nor am I providing legal advice applicable to your particular needs.
This is an area that I have some experience in -- I've gone after several websites that have done this exact same thing with online character/account sales. It depends on the site; it also depends on where the owner is. I'd be happy to discuss further with you directly.
The author is a Maryland attorney; however no answer given on Avvo is intended as legal advice or intended to create an attorney-client relationship. Dan's expertise lies in the electronic entertainment (video game) industry, as well as complex internet law issues, electronic free speech, entertainment law, copyright and trademark law, and computer fraud. He primarily represents game developers and founders of emergent internet technologies.