You should understand that there are two models for pricing service. In the flat rate model, each job is quoted. $440 for job A, $300 for job B, $510 for job C. The shop has to be prepared for the possibility you will say "only do B," or that you do them all. If there is overlap, or the tech is fast and gets the work done in less time than the bid would suggest, the shop wins.
If the tech is slow he or the shop lose out, so they have every incentive to bid so they won't lose while not bidding so high that they don't get any work. That is the most common scenario for auto repair, and if you agreed in advance to the prices for A, B, and C you have little to complain about re the time it takes to do it since you agreed in advance.
One problem with that approach is that we often encounter surprises when doing work on older cars; things that will take more time to address. If you are working to a bid number you just let that stuff go, knowing it's not part of the job, and they can come back later and tackle it. However it often leads to scenarios as described here where a shop fixes A,B, and C today and D breaks on the way home but could have been addressed if not on a bid.
The alternative is to say everything is billed on a time and materials basis. Shop does whatever you ask, and if they find other problems and you want to fix them, the final bill is simply the total hours worked and parts used. The difficulty some have is that the final cost isn't known in advance, but I contend that you can't know the final cost of most repairs on older vehicles anyway, since you can't anticipate everything on older cars. You have to have a shop you feel is trustworthy and capable to follow this method but it gets better results.
The proof of that is the fact that the first method - flat rate - prevails in shops that cater to a throw-away culture; fix the car until problems pile up and then get another. Time and materials is the only way the restorers who show winning cars at Concours of America or Pebble Beach work, because that level of craftsmanship is not sold on a bid basis.
Most people are not at either extreme, but it's worth thinking about
