I disagree. If you treat people like that you will get a really bad reputation in no time, then no one will wnt anything to do with you, this ain't ebay.
On topic:
I would think a reasonable amount of time to wait is 24 hours to reply to your email. I have no idea what you are selling, but you need to be clear and reasonable in your terms. I've seen "Payment within 1 hour of I'll Take It" is pure BS, and I always pass on those threads, as do many people.
If it's been more than a couple days, then I'd say you got a flaker on your hands. In which case, wait the 2 weeks and relist it or resurrect your thread. You can't bump it, but you can see if if you sort by last post.
As far as leaving feedback is concerned. No deal was done, no money changed hands, no product was shipped. There is no room for feedback because nothing happened. As infuriating as it might be, you aren't out any money or a knife, but gained a little frustration. Make a mental note of the buyer and just move along.