I do a good bit of buying and selling on Craigslist, and there are a few simple rules I always follow when making a deal.
I always have two copies of the bill of sale, both get signed, and I keep one. I also write down their phone number on my copy,and I always jot down their license plate number as well. Most times I catch the plate number as they pull into the parking lot so they dont know, but sometimes I have had to resort to going and looking with them standing there. Both copies get the serial number recorded on the receipt as well as the purchase price.
I always meet in a public place where there are lots of cameras and lots of folks around, and I pick the time of day.No late nights, dark parking lots,etc
I never carry cash in my pocket, its kept in a locked box in the truck.After I look the item over, I make an offer, and if they accept the deal I leave the item on the hood of the truck, retrieve the cash, and make the swap.When I turn to go back to the truck to get the cash, they can plainly see the 9mm in my waistband under my tshirt.
When I get home, I attach the bill of sale to all printed out copies of the craigslist ad, as well as all emails from the seller/buyer and they are filed away.