One difference with auto repair: I expect the garage to call me before they do any work that exceeds the estimate.
It's not just an expectation, it's the law in many places. When I was a pro mechanic in Indiana, anything over original estimate + 10%, and authorization from the customer is required. Well, not required I guess, since if you show up and the bill is 20% over, you just pay the original estimate. (Yes, in the worst case you might have to sue to get your car back. Personally, I've never known that to have happened, because most shops aren't looking to rip you off.)
But, as you point out, me being in the middle of a top end job is a little different than a surgeon who's working on a running engine when it comes to needed extra work.
It's not just an expectation, it's the law in many places. When I was a pro mechanic in Indiana, anything over original estimate + 10%, and authorization from the customer is required. Well, not required I guess, since if you show up and the bill is 20% over, you just pay the original estimate. (Yes, in the worst case you might have to sue to get your car back. Personally, I've never known that to have happened, because most shops aren't looking to rip you off.)
But, as you point out, me being in the middle of a top end job is a little different than a surgeon who's working on a running engine when it comes to needed extra work.