I don't setup the bikes like they are my own. Most customers wouldn't come back if i set there bike up for 5'5" guy with unusual taste for abnormal setups.
I know what your getting at though. By treat is as if it were your own. When repairing bikes you should ask yourself epistle you ride it in the condition its in.
Although that depends on what you are used to riding. If you ride a 20 year old raleigh covered in rust, i would guess the standard would be low.
Key to being a great mechanic is knowing what new feels like and what current trends are. To get the bikes to feel and look right.