If it's not on the list, you don't get paid for it. However, sometimes it's easier (on a brake job for example) to just replace everything instead of trying to figure out which part was below the minimum and putting it back exactly where it was. I do this if I'm grinding xp and just want to get it done fast. Besides, as a former real life mechanic, there's no way I would ever put used brake pads on a brand new rotor, or a used clutch disk on a new flywheel. As for XP bonus, I don't know why some jobs have it and some don't.

thanks for that

For the non story orders you can be picky which ones you take, so only taking the ones that have the bonus's and skipping fluid only jobs, get a bit better XP and get to level 30 quicker.
For really fast XP you can completely strip and rebuild jobs just using the parts it came with and only replacing the bits on the list.