I had an experience where I pulled in at the 1st (private) CG that was available upon getting off the interstate @ about 11:30 one night.
Didn't unhook, just crashed for 5-6 hours and was hookedup and snooping around the office at 0600 the next morning..no sign, no number, no "nothing".
Not knowing any better, I get an envelope from the truck to put some $$ in when a guy pulls up behind me, tells me to hurry up and that we had to be out by 6:30 or the office would be open and we'd have to pay. "Say what?" says I
This guy apparently came to this park frequently after 10:00 (closing time) and left before 6:30....all without paying. He continued to get huffy when I took another 5 mins to put $25 in an envelope and slide it under the door.
...so it happens at least once.