Well, I tend to find (in our group) mistakes more likely than deliberate meanness, as witness the fact that people often over-charge themselves! What is the last digit on the Hobbs meter? In our plane we book by tacho time, and the last digit is 1/100 of an hour, and I'm not going to get hot under the collar about rounding up or down by about half a minute. Maybe someone inadvertently wrote down the time before stopping the engine...