Charges in error happen more than I would like.
This is one reason I check the bill and make all corrections before leaving the hotel with a printed receipt in hand. The last "error" was in Vancouver where we had complimentary full American Breakfast. On checkout we were charged for the breakfast, we were told that we were only entitled to a Continental Breakfast. We had our confirmation that proved otherwise and the Hotel stated they would make the correction and mail us the corrected invoice. Trust me this doesn't happen. They were insistent that we move along and they would take care of it later. We stated we were not leaving without a printed receipt that we were paid in full, they reluctantly did it. We have been burned in the past for invalid charges and it takes a lot of work to unravel it after leaving. I have found that getting it straightened out before leaving is the easiest "fix" in the long run.