If the item is as described and works fine, you should buy it. You should do your homework on the item ahead of time to know what to expect. It isn't cool to waste people's time to 'window shop' or to learn about the item in general.
But if it is misrepresented or broken, go ahead and walk away.
I sold a G1 firewire ipod once and the guy was all excited and drove 1.5 hours to come down and get it. When he saw it he said, "wow, this is an old model" and "it doesn't have usb?". I posted clear descriptions, photos, and model numbers on craigslist so there was no chance of deception. He eventually bought it, and then had to buy a $50 FW card for his PC to use a 5 year old ipod
, but I would have been really upset if he didn't buy it. You have to do your homework as a buyer and not be so impulsive. Craigslist sellers are not Walmart!