If I broke something, I would not charge an additional amount.
One of the meanings of "estimate" in my dictionary is "a statement of cost of work to be done." I think that is the definition that the California Bureau of Automotive Repair uses. A shop can not charge more than the initial estimate unless the customer approves it. If I were given an estimate of $200 to change the spark plugs, and the shop called to say they broke some of the plugs and wanted $1000 to do the job, I doubt I would approve it.
exactly, they cant just tack on whatever they feel like, since you did not authorize work. the shop does need to get approval prior to work, or they can get stuck with it. i though you were saying they should stick to their quote no matter what.