I think the safest thing is to simply refund people who have done nothing but post in the NXTL threads as those people will be hard pressed to argue that they are legitimate users if they simply registered an account, sent a payment to NXTL, posted their account numbers and then never came back again. There are quite a few like this. It won't eliminate all of the sockpuppets but it will get rid of a good chunk of them without harming any legitimate users.