I once came home from work to find that the British Gas service man had condemned my water heater as unsafe, and illegal to use on the grounds that it was installed with less than the regulation spacing between the flue and the boiler flue below it. When I pointed out that it was British Gas that installed it, that the boiler was in place at the time they did so, and that they'd never said anything at any of the previous service calls, they decided it wasn't unsafe after all.
I once asked a service man to check for a CO2 leak because there were sooty marks on the wall around the boiler flue:
"What do you want that for?"
"I wouldn't worry about it, it's probably ok"
"...well I haven't got anything to measure it with anyway"