I've sold a few parts here and on another car enthusiast forum stating that paypal friends and family is the only online payment method I'll accept, and people have been OK with that. But soon I'm sure the IRS will put the squeeze on that method too.
I remember an episode of the old show Married with Children where Al and his neighbor Steve restore a Mustang, and in one scene they meet some shady character in a back alley to buy a mint ashtray for their project. Funny scene but sadly in the near future I'm afraid that is what it is going to come to when buying and selling vintage car parts!