I wrote earlier that I was asked to show my logbook (other than to qualify for professional status) only once, and that was about 20 years ago in Australia. I was on a liveaboard, and the crew wanted to get an idea of diving experience in order to assign buddies, etc. Some of the other customers did not have a logbook. That was just a minor inconvenience.
For that trip, the dive operation was trying to make a living. My wife and I had booked many months ahead of time, paying a premium price for the premium cabin. About half the other customers were recruited from off the docks in the days before we sailed, likely paying a fraction of the standard price. These people did not have log books with them, and you can bet they weren't going to be thrown off the boat for that reason.
For that trip, the dive operation was trying to make a living. My wife and I had booked many months ahead of time, paying a premium price for the premium cabin. About half the other customers were recruited from off the docks in the days before we sailed, likely paying a fraction of the standard price. These people did not have log books with them, and you can bet they weren't going to be thrown off the boat for that reason.