I like to think that I have a good amount of experience with buying and selling on craigslist. Bought my first car from craigslist back in 2009. Since then, I have bought and sold another 5 cars and 4 motorcycles. My wife and I also sold all of our 'stuff' on craigslist when we were downsizing earlier this year. I have honestly found that text messaging seems to be the quickest, and most effective way to communicate with a seller. The van I just bought last weekend I made the deal over text from 450 miles away with a 60+ year old man! As a previous reply mentioned, I always offer what I think the vehicle is worth up front. I do my homework/research, and if they are asking $5,000, but the van is only worth $4,500, I will be straight with them and offer that letting them know "if everything is as good as you say it is, I have $4,500 CASH right now and can come pick it up". Then if i get there and it is even worse in person and has issues they didn't describe in the ad, then i may offer $4,000 explaining that i would be taking a risk and/or have to do some work to it before i could safely put it on the road. Or if it is real bad, i walk away.
Most, if not all, people i have dealt with on craigslist are very nice people who just want to sell their stuff for a fair price. So I always go out of my way to be kind, calm, and courteous even if the deal falls though.
Hope this helps some!!