When I was turning a wrench for a living, the standard industry practice was 30% markup from what we paid, which was called the ‘jobber cost’ at the auto parts store. That 30% is for more than just profit. A shop ends up ‘eating’ a certain number of parts for a number of reasons, so you need a little margin on the parts you handle to cover yourself.
The price you see on Rockauto or similar discount on-line stores is pretty close to jobber cost for most parts. Therefore, if you paid something on the order of 130% of the Rockauto price, that is in line what what you would pay any other shop.
What frosts me is going to a dealer and paying three to four times online prices for the same part from the same manufacturer that I could get on line if I did not have a car in pieces all over my garage and was willing to wait a few days.