True,it is very annoying to receive what you would believe to be a firm price only to find out upon teardown of your car,at which time you are Firmly comitted,the price has changed.I prefer to quote higher up front,explain the possibility of unforseen or forseen difficultys,Then, offer the appropriate discount or reduction in price when the job is completed.I have Never had a customer upset with a bill that was LESS than originally quoted.This Must be explained beforehand, otherwise you will not get too many jobs as your prices may seem a tad high !