Lets say the refueler lives 10k or so from Airport.
He has to put on PPE, drive to airport, get the tuck out, deliver the fuel, complete paperwork, put the truck away, secure the yard, drive home. Not to mention the DAMP requirements for 0.0 BAC which effectively means if he / she is on call, they can never have a drink.
YJPT, you summed it up nicely. And it depends on whether the refueller is on a salary or gets paid on a commission basis like I did - a lousy 5c a litre. That was about as far as I had to drive for an a/h callout, so you can see that if someone rocked up in a Jabiru & only wanted 20 litres I would be well & truly out of pocket if I didn't ask for a callout fee. I never charged more than $30:00, if additional aircraft turned up while I was dealing with the first one then the fee was split between them, & I always offered a receipt for the amount if required.
I never charged callout fees to the RFDS or any medical flights such as the Qld Government jet which used to drop in on its way to W.A. to pick up an organ for transplant, the Police Airwing, any search & rescue aircraft or military aircraft either.
DF.