Cash works, but only if you're close.
I have bought a couple of machines from California and a couple from NY. As much as I would like the adventure of driving to bring home a pin I don't have the time to make those road trips. I paid by direct wire transfer. I only bought from people who had been on Pinside for Several years and had a multi-year track record of sales and good reviews. Everything shipped via STI. Never had a problem.