I've made plenty of such deals. Most often the hours just worked out better; they were working during the day, or I was in college and had class, or I'm working during the day, etc.
I typically bring along a buddy for FTF deals. More to kill the time on the road than anything else, but it's nice to have backup if you need backup. In reality, though, not being able to get a friend to ride along has never stopped me from completing a FTF sale with a stranger, and that applies to guns as well as any of a number of other things. I'm no less armed doing a private transaction than I am at any other time of day.
To be fair, though, I'm usually buying more collectible stuff. WW2 guns, old colts, stuff like that, so RC may have hit it on the head. Still, a trade for a '44 walther ppk brought me to what would have otherwise appeared to be a shady situation: dark van in an unknown, not particularly nice neighborhood, with not particularly well dressed folks, edging in on "gangsta" duds. We ended up chatting about milsurp guns and the like for the better part of an hour. I walked away more confident in something I've long suspected; gun people are generally pretty civil to each other. An armed society is a polite society, indeed.