Lots of myths regaring glory holes. Probably a lot different in major cities vs. those in truck stops. lol. I don't think all of them are 'that' anonymous. Many times the cocksucker(s) (the one wanting to service) is standing around outside the booths waiting for "the cock" (the one looking to get sucked) to come into the arcade, the cock sees someone who is interested(ing), makes eye contact and signals perhaps, then goes into a booth. The cocksucker then goes into the next booth. And whatever happens happens.
It could get pretty expensive for someone to wait inside a booth and feeding the machine money to keep the video going and wait wait wait for a cock to come through. So it's not always about someone sitting in a booth waiting for an anonymous cock to slide through. Also, if there is someone in the booth waiting, the cock will look thru the hole before closing the door to see if someone of interest is in there. Vice versa too, if there is a guy in a booth with a hole jerking off, you can look thru and see if he is someone you want to suck. Not every guy will take any old anonymous person, and that goes for both persons (the sucker and suckee). So basically, an old grandpa isn't always getting the treat of sucking off a hot guy, because both parties pretty much know who is the sucker and suckee . But of course, there is a certain amount of anonymity in terms of just getting off with someone you dont know and can leave when you get off or in mid suck if it's not working out.
Honestly, its not a helluva lot different that going to some club, seeing a guy you are hot for, being horny ad wanting to either suck or get sucked, taking him home, doing it, then leaving in the night. LOL. Really not a lot different.