Met with customer and quickly informed him of the trip fee and diagnostic charges due. Customer paid me $505. In cash. I explained that their would be additional charges if I found anything wrong. Spent a few minutes going over the unit. Light the unit and it stayed on. Observed the operation for several minutes and all seemed okay. Came back into the home to explain to the customer that there was an additional charge for lighting the unit, and he became very irate. After explaining things several times he opted to call the office and speak with management.