It comes down to taking the chance or not.
In spite of the thrill of having a spontaneous encounter with a stranger, I'd be more inclined to meet a guy at least one, in public and with no pressure, and make judgements. Generally speaking, married guys are the most likely candidates because they can't have an STD at home (among other reasons). Look for a ring or a tan line where one has been, maybe pictures of wife/kids. Be prepared to show the same.
See if he keeps himself clean and groomed, and weed out any slobs, of course.
If everything goes well, make plans for another meet in a private environment.
There's not much more you can do at that point.
I will mention that it is possible to have a guy ejaculate while holding your mouth open and letting him shoot into it, but I think if you're going to swallow it, you might as well suck it.