I had previously thought that the OP's account was hacked and/or sold as it's recent activity has been somewhat suspicious as of late. This is especially true considering that the OP is currently selling his signature to someone who has negative trust for running a ponzi....although the OP may simply not care about this.

I am curious if the OP is able to sign a message from an old address associated with his account.

Either way, it does appear that it would be a bad idea to accept any kind of reversible payment method from the OP, and would probably be best to use escrow when dealing with the OP.