This happened to me when I returned one very loved 3 year old C Class. They tried it on to the tune of £180 of which £35 was for the engineers report! I witnessed the car being inspected. Unforunately it had rained - thus the car was wet therefore apparently preventing a full inspection.
I disputed a tiny door 2 door dint and 1 chip in the windscreen. I argued that the damage they alleged was well within the fair wear and tear guidelines they sent, and that I had photographic evidence. I also disputed the quality of their photographs and informed them that they had been taken in a misleading way thus to make the damage look worse than it was! Plus the measurement marker was not against the damage thus one couldnt see the extent of the damage they were claiming!
They backed down, and set me a cancellation of invoice and a letter with an apolagy. :bannana:
They do try it on believe it! Just be prepared.