I have one more thing to throw in here. Let's say you have an intermittent problem on your vehicle,say a .........'02 Dodge Caravan and it doesn't want to upshift sometimes. You might have to drive it a whole day to get it to do it. Would you rather a shop put one sensor or part on ($50 -$200)and then let you drive it to see if it fixed it and then bring it back again if it still does it,or would you rather they replace everything possible (maybe up to $500-$600)that would cause the problem and the problem be fixed?
Thanks everyone for their replies.
I would explain exactly what you said here to the customer using a little different verbage. Something like this:
"I think that the governor pressure sensor, the part that tells the transaxle when to upshift, may be intermittently failing. However, without the sensor failing while it is here in the shop, it is difficult for me to diagnose the problem completely. I can try replacing the sensor for $xx and let you drive it to see if it is fixed, if you wish to go that way. Or I can replace a number of components that may cause the problem for $xx and that "should" take care of it".
In my experience, I have found that customers appreciate the fact that you are willing to try and save them some extra money as long as they can be without the car for a couple of days. Although changing many components may fix the problem, I agree with Rooster that shotgunning it may not be the best approach. I would rather figure out the exact cause of the problem, even if it meant using the customers car as my daily driver to get it to fail. Then if a prospective customer calls on the phone with similar symptoms you would be ahead of the game and could speak confidently in regards to their symptoms, your previous experience and then worst case scenario (replace many sensors/solenoid pack etc.). In the end, I think that finding out exactly what the problem is would make for a happier customer and would also increase your business and personal knowledge.
Intermittent problems are a pain in the a__
Although not applicable in this scenario (probably), when customers could not leave their cars with me, I would try and setup an indicator (test light) or gauge on the system/circuit I suspected was a problem and have them take the car (when it did not involve an issue where the car would leave them stranded). I gave them the instructions to check the gauge or test light when the problem occured and call me immediately. In almost all cases, the customers were happy to do this since it gave them a sense of being involved in the repair as opposed to being at the mercy of the technician/shop.