The engineers have a device called a Ramp Damage Checker. It is an ultrasound device, very simple to use, and will indicate to a line engineer whether or not specialist investigation is required.
So a baggage / waste-water / catering guy has a ding with the fuselage and notices no obvious signs of damage and decides not to report it (maybe because he is on the minimum wage or some other rediculous conditions and is worried about the implications). No problem.....the engineer will obviously pick-up any unforseen damage pre-departure with his pocket device,
AKA - the "Ramp Damage Tester". Totally awesome!!!