I've been working on various types of pianos for 50 years.  Early 
on I decided that it was my fault for missing certain issues, and 
I compensated for that by estimating on the high side before going 
into the instrument.  

This did two things.  It saved me from feeling cheated, and it saved
the customer from being angry if I were to ask for additional funds.
Usually the end result was that I gave the customer a reduced bill, 
which got me much more business in the form of referrals.  

I'd tackle almost anything, and still do, from new soundboards to
making metal parts in my machine shop.  It's been a good trip!

Tom Binnall