Not only should you ask to see them but have them show you the new parts they put on the car and do a visual comparison to make sure that they are the same (an old shyster mechanic trick is show someone else’s old parts). Since you’ve already done your homework (see last edition) and gone online to check out what the parts look like, you know exactly what you are looking at (ok, maybe not exactly but you have a good idea…ok, parts may look different from car to car but you have a general idea). While they’re showing you what they’ve changed, take the opportunity to ask numerous questions about why they had to be changed, how do they all work together, is it something that needs to be changed periodically (I’m sure you’ll think of a few more, just keep asking). The more informed you are the better off you’ll be.
The thing to remember is that you are taking the upper hand here, the bottom line is you’re holding the money and they want your money.
Any mechanic that will not take the time to explain what it is they are doing is probably doing something shifty. Don’t let them get away with it.