I think you're on the right track.
The customer needs to be told, up front, on the phone, your fee to respond. That fee ought to cover a minimal amount of time; say, one hour of troubleshooting / diagnosing.
The problem with that is, there are different levels of trouble shooting, that is why you can.t include the dispatch fee with the trouble shoot, we tried that years ago and always lost out, some trouble shoots like an outlet not working, can be an easy single room one outlet or the mullti room multi outlets, a big difference in the time requires to trouble shoot.
