Service call and diagnostic fees, done right
The diagnostic fee is the bouncer at the door. Charge it confidently or expect a stream of price-shoppers.
Charge enough to cover the trip
A service call fee that doesn't cover drive time and the tech's hour is just a discount. Set it to make a trip worth taking.
Apply it to the work or don't, but decide
'Waived if you book the work' or 'always charged regardless' both work. The mistake is improvising. Pick a policy and stick with it.
State it on the booking call, every time
Surprises at the door damage trust. 'Our diagnostic is $X, applied to the work if you go forward.' One sentence.
Take your version of this question further
This is one operator-tested angle on the question. Your shop, your size, your trade, and your team change the answer. Ask your specific version inside Ask a Shop Owner to get a response grounded in how owners like you actually handled it.