For something like tickets I can see not expecting to negotiate when you meet but for physical things I can see them wanting to change the price after actually seeing it.

People don't always give good descriptions or pictures so you can't tell what something really is like until you see it.

I have purchased several things on craigslist and I agree it takes a while to get meeting places figured out but I just figure not everyone is as connected as we are. I know people that don't even check email once a day