Its not uncommon to be charged for Shit not done... always hear people marking fuel/air filters, adjustment bolts with white marker and nothing has been touched.
Bloke on this board bought my GQ, put it in for a Pre Trip inspection, had it done, then had a few mechanical issues, put car offroad for few weeks, got going again, then got no more than 20klms from the place, and the brake pads were that worn they fell out.. rooted discs, and more... shop told him to intercourse off.