If you buy something off CL that you think should have sales tax who do you give it to?
CASH also means no receipt, which surprises some people.
But if I have a signed receipt from you, I can prove that I bought it in good faith and that you sold it to me, claiming that it was legally yours to sell (assuming that I use my normal receipt which has a picture of the item from the ad and which states that it is sold as is, where is and is to be removed immediately).I don't see that as any proof at all. If it came right down to it, you would be in possession of stolen property one way or another.
I can sell you the Brooklyn Bridge and make up a pretty nice looking invoice on my laser printer. lol
I have scribbled Fred Ziffle on a piece of paper and 555-1212 as the phone number, or some such thing. AND asked for similar documentation for tax purposes, because I realize that it is inappropriate to ask for a receipt in the underground economy. Generally, you pays your moneys and takes your chances. If you don't like that, best shop at the MALL.