Disappointed for additional charges

The car is ok. But very disappointed to pay additional 1000 baht for repairing a tyre. When returning the car, the staff found a nail on the inner part of one of the tire. The place normally will not be notice / checked when collecting car. So, I didn't know whether the nail was already there when I collect the car or it is due to my driving. When returning the car, the tire looks perfectly fine, no leaking of air, and I had no problem of driving whole day back to the return. And we have be there talking to the staff, her leader for almost an hour, and the tire had no sign of leaking air at all. So I really doubt if the nail was already there when collecting the car.