I'm fine with cash sales, but it's a royal pain in the ass acquiring large stacks on short notice, and I do NOT like driving around with wads of greenbacks for reasons others have mentioned. I get that people suck and scams abound; it's also not really that difficult to vet people.
It works both ways, too - while I've done large cash transactions, I've pulled out of more than one because I didn't have enough trust to show up with 10k. Bring a gun and a buddy if you want, that doesn't matter for shit if someone's waiting for you on their turf and wants what you have. But cowboy yourself to sleep at night if ya like.
I would never take a personal check, of course. Couple grand as good faith and PayPal/zelle is fine by me most times though, IF I can vet you to my liking. If I can't, I don't give out my address regardless of how much you claim to be bringing. If we have history, or a really good rep, electronic only is fine.