This kind of thing sucks and as was noted this is a fraud issue not really an NFA issue because the best reasonable result you can hope for is to try to recover some or all of your money. While I am not going to say it is impossible to get a judge to make a ruling in your favor against the BATF, I would say its not worth the time and expense and such a ruling would most likely be appealed even if successful (remember this is not a criminal prosecution against you). Also, the reality of the situation is your would be advised to find and hire a good attorney his home state to look into his assets etc. (does he own a home, what is the status of the bank account that was used for the sale, tax or other liens against him etc.) to make a decision if it is worth it to go after the guy. If it looks like he has assets you should sue him personally where he lives (the corporate form does not shield people from fraud even if you bought from a business) and hope for the best. As an aside, I wonder if I know your brother (I started in med mal in Boston a few decades ago but moved on to other things - that is another story). I hope it works out.