Forge a receipt, nothing elaborate, just a sold as seen, cash paid and an indecipherable signature.
FWIW I always get the buyer to sign the duplicated receipt with time and date on it.
Tempting, but I fear consequences -- if a copy of any receipt gets shown to the rightful owner, he may be able to use it against me in some way. Then I could be looking over my shoulder indefinitely.
Also, I'm not 100% sure I got the surname right when I eventually did register it.
Plus, from what I've gleaned on social media, I've got reason to believe he's got some dangerous connections.