And that does indeed happen, the same as those blue badges. I know someone who uses his fathers blue badge and his car all of the time.
I've had access to a BB, for many decades - first my partner, a few years gap, and now for me. They are not easy to get, you have to list your issues, have them verified by a doctor, and have an interview at a centre to prove need. In all of that time, and use, only once was the valid user ever checked...
I had taken my partner to Selby shopping, parked out the way, on the road side near the centre, where I had often parked before. On the way back to the car, she had nipped in a shop, just round the corner from the car, I had continued and got in the car, all seen by a parking attendant. Over he came, and asked to take a close look at the BB, which had my partner's name on it, obviously not me. He asked why I was using it, I said for her, and she was just a few minutes behind me. He waited, until she turned up, was satisfied, and I said 'well done, more checks should be done on misuse of the BB's'.
No doubt some people do get a BB, by swinging the lead, but I think the main problem is misuse of the BB, by friends and relatives. Nobody, but nobody, is bothering to check the user of the BB is valid. My one check in 40 years, seems to confirm this lack of checks on use.
Supermarket BB parking misuse seems to be much worse - everyone seems to think it's fine to park in the disabled spaces, and nowt much anyone can do about that.