from forkingabout "It annoys me when parts get replaced / money gets wasted because people haven't a clue, they always seem to get found out for being useless in the end sooner or later."

My sentiments exactly and double on the last sentence.

My cynical response is:
If you are a dealer with some corporate backing, offer some FREE factory training at the customer's site to rectify the problem.
Otherwise, accept the fact that the "technician's" shortcomings may be a product of his company's management shortsightedness.
Inept managers beget inept workers in a lot of circumstances. And if nobody in the chain of management can recognize inefficiency (or on the other hand, proficiency), the company is destined for some hardship, if not outright failure anyhow.
The thing about inept people trying to hang on to a position is that while they KNOW very little about the job they are supposed to be doing, they often THINK that any suggestion to make changes in their area is an effort to remove them from their position........they are already paranoid to some extent and an outsider offering unsolicited advice is rarely received in a welcoming manner.
Now if someone from management at that company asked (however pointedly) you questions concerning why "such and such" a part or component seemed to always need replacing or why it always takes an entire group of parts to get a truck going again...................that would be an invitation and opportunity for you to set things right. Unless you are personal friends with high management in that company, it might be best to wait until you are asked for an answer or opinion.