My only experience was from our visit to Las Vegas last week...

Brenda and I flew into the airport ... we didn't drive. I know nothing about "change machines" or "meters". We retrieved our baggage from the carousel in the airport and walked directly to the busses. There were at least six busses in line waiting for car rental passengers (like a fleet of taxis). If you try to board one of the busses in the middle of the line, you will be instructed to get on the first bus at the head of the line. Seemed like a very efficient operation to me. Of course time of day may have something to do with it. We liked the change... and the busses were brand new. Some of the old junker vans of yesteryear left much to be desired.