I've sold countless items over the last few years and generally most people who say they will have have something do buy it, but of course there's always some that don't ever get back to you.
I don't usually mark as sold until payment is received in case they don't buy it.
Only problem is you then get other offers which you have to reply to explaining the situation. Bit of a pain but not a big issue.
Certainly beats eBay for all concerned
