Sometimes, you'll fix a problem only to prove that there are more things wrong.  I have been working on a guys walk-behind mower now for a few weeks, off and on.  I first showed up, he had overfilled it with oil.  I drained the oil to an acceptable level, ran the mower till it ran clean and called it a fix(no problems arose).  He said it ran for about 30 minutes and stopped.  I checked it out and found the carb had some dry gas in it and the float needle was sticking.  I cleaned out the carb and it ran long enough for him to mostly finish his yard.  Then it stopped working again.  I think the carb had some dry gas inside some of the small orifices and they got plugged up as it ran longer and vibrated some of that junk loose.  Now i'm in waiting for the new carb to arrive in the mail so we won't have to worry about it anymore.  
The biggest problem with trying to save the customer as much as possible is that it ends up coming out of your overhead.  If I had just had him replace the carb in the first place, like most would have done, it would have fixed the problem and cost me less and him the same(in the end).  But had the carb cleaning done a good enough job, it would have cost him $40 less.  I find it hard to replace before I try to fix.