Auto repair diagnostic fee: how do shops explain it without losing customers?

The diagnostic fee argument comes up all the time in auto repair. A customer sees a warning light and thinks scanning a code is the same thing as diagnosing the car. Then the shop has to explain why a tech spending real time on testing is not free. The hard part is saying it without sounding like you are charging just to look at the vehicle. I have seen better results when the advisor explains th…