Just thinking aloud.
Is there maybe some way to make a private auction on an auction website? They should offer some protection for payments and such. That doesn't help you get paid safely but it does make it a more businesslike transaction.
Otherwise, someone once suggested Bitcoin to me as the closest thing to an anonymous payment you could get. That would necessitate a whole bunch of cryptocurrency research and some of the advocates for it are... a little enthusiastic.
Yes, I've started selling my used underwear as well, at a SERIOUS discount! (2 for 1 - that kind of thing!).
Unfortunately, my customer base is turning out not to be the one I had targeted but rather one which I would tend to avoid more than mere casual contact with! Oh well, money is money!!!