It sounds like the drivers might be used to including the tip in the receipt, because, sadly enough, I am sure that most other patrons would want to be reimbursed for the full amount, including tip. It could be that Autopac would have the same consideration, too. They are probably thinking that they are doing you a favor....wrong assumption, but in this day and age, honor isn't all that common
For the record, I applaud your honesty
For the record, I applaud your honesty