When I worked 'at one of the London airports' there was free motorbike parking just outside most of the car-parks, usually covered, but not totally secure so a good stout padlock and chain was required. Knowing that the car-park charges were horrendous and a complete rip-off we had a simple plan to 'stick it to the man'. If somebody was going away for a few days they would park their car in the car-park, and since we knew when they'd be coming back (which flight, time, etc) we would go into the car-park via the barrier that day and collect a ticket. We would meet them once they were land-side and give them the ticket (we we had gotten about an hour earlier) and the would pay for 2-hours of parking inside the terminal!
Probably wouldn't work now because of the need to enter registrations, and for those to match what is seen on the camera at the exit barrier, but it all worked well for several years.