The odds are slim that you would get caught using GMRS radios without a license. The FCC does not travel around and monitor frequencies like they used to. However if someone files a complaint that is legally licensed the "men with the gold badges" could show up and they will hurt you...financially because their fines apply to each radio and each frequency that you have illegally. They are non-negotiable and always win so they can justify the trip. Take the chance if you want to. I don't want to so I got my GMRS license. A few years ago the busted a sheriff's office in southern California because their license had expired. Their fine was around $250,000.00.
I doubt they "always win," there is an appeal process in place and the fine(s) if any are based on their ability to pay. Sure the maximum fine may be $XXXX but if the guy is living in his car on $100 a week unemployment they're not going to get $XXXX. He will NOT be seeing any jail / prison time for transmitting on a GMRS frequency with out a license. Just saying!