The call that costs you money before you arrive
A forty minute round trip at a burdened cost of sixty five dollars an hour is already forty three dollars gone. Add fuel, add wear on a van that will need tires and brakes sooner because of that trip, add the share of your monthly overhead that this call has to carry, and you are well past a hundred dollars before you have picked up a meter.
That is the number most shops never work out, which is why so many of them charge seventy nine dollars for a service call and quietly lose money on every diagnostic that does not turn into work. The fee is not arbitrary. It is arithmetic, and the arithmetic is not close.
What to do with the result
Treat the recommended figure as a floor and then decide how you want to present it. Some shops charge the fee and waive it when the customer approves the repair, which works fine as long as the repair price already carries the trip. Some charge a flat diagnostic that is clearly higher than the trip cost and never waive it. Either is defensible. Charging less than your cost and hoping volume fixes it is not.
If the number comes back higher than your market will carry, the lever is usually not the fee. It is the calls per day. A tighter route, better phone screening, and parts stocked on the truck all raise the number of calls each day of overhead has to cover, and that drops the per-call share faster than anything else on this page.
The free estimate line
The last figure is the one worth sitting with. Three unpaid trips a week is not three trips, it is over a hundred and fifty a year, and at typical costs that is real money walking out the door annually. Free estimates can still be the right call for large replacement work where the job value and your close rate justify it. For diagnostics and small repairs they are usually a habit rather than a strategy.