That’s a great philosophy Pete unfortunately it wouldn’t work for me anymore due to the fact that nearly every garage has a code reader and as such are filtering out the “easy” jobs. Mostly what I’m seeing is the cars that have already had this that and the other changed by other garages that are only going on the fault code readers description; and are not secondary testing to prove the fault. As such I charge out on an hourly rate, and try to explain the diagnostic procedure as the repair progresses. The problem with the Agila was that I had correctly diagnosed a faulty EGR valve not realising there was another underlying problem. Now trying to explain that to a non technical patron is a pretty (if not impossible) hard thing to do, he also had a major service and rear crankshaft oil seal replaced; so he spent a couple of pounds with me. I find as my experience grows I have to dictate the possible avenues of repair that I may have to go down with the customer and possible expenses that may be incurred, trying not to scare the customer away, which is quite a juggling act! And sometime as you say; to keep good customer relations, I just have to swallow the extra expense (unfortunately)!