Almost all parts that any type of service person installs has a markup. Auto, HVAC, Plumbing, Electrical, small engine, tractor it doesn't matter. It is just part of it. If you walk into a supply house you are liable to get a price swing anywhere from jobber/wholesale cost to well over retail if you piss off a counter person.
An example if you go into a auto part store and buy a filter for $4.99 it may say list price is $7.39 that is likely what a shop would charge you if they installed it. While they bought it anywhere from $2.50-$4.00 depending on how much they buy from that supplier.
If you walk into an HVAC supply house and buy a start run capacitor they may charge you $25 bucks. You could buy it off ebay for $10 while the HVAC guy could buy it for $8 if he has an account at supply house. Then he will charge you anywhere from $40-$100 bucks for it. If its a Saturday night at 11pm and you just gotta momma cooled down. He knows that but he had to take time away from his life to do it. It also depends if he charges a service call or does flat rates for different items. Its all just part of the way it works.
Supply/part houses make money from their business accounts not guys coming in buying one breaker or small part once every few years.
Tradesmen are no different than anyone else. If you have worked years to learn a trade you want to be paid for your service you provide which includes your ability to do it quickly and right the first time. Its no different than a guy that has been an accountant or lawyer for 15 years. Knowledge and skill is acquired over time.
There are many different prices for everything. When I worked for an auto parts store I had to determine the status of the customer before quoting prices. They had eight different prices for the same item. Wholesaler, distributor, stocking dealer, dealer, jobber, shop, and full retail. We had one tier of discretion on good customers with large orders but had to have supervisor approval. Depending upon the item, we could have a 300% to 30% margin.
When I got out of H.S. I sold parts for a while. I got in trouble once for overriding a price and charging a guy more than it was listed for. He was a jackass and kept arguing over a valve. He called asking for an intake valve what he brought in was the exhaust valve. I sold him what he had in his hand but at the more expensive price since he was a jerk. I put in the override (customer was a jerk) next day boss said corporate called him and wanted an explanation. I said "I thought it was pretty clear in my comments." They had never seen anyone use an override to increase a price before I guess.
Yesterday I replaced my front rotors and brake pads on my 04 impala, saved myself about $100 or so. The bolts that held the caliper bracket on were a mofo to get off, had to use a 1/2 driver breaker bar and liquid wrench to get them loose.
Today's, well, started today but who knows how long this may take, workin on chit project. Some kind of binding and clankin goin on in the transumission. Also on this weeks workin on chit schedule is a 2" lift on a jeep for a neighbors daughter for Christmas and putting a new clutch in my personal truck which is the same one that got this thread started. Any y'all that see any of my workin on chit threads know I gotta use this rollin and winchin elevatorizer. It makes a fine atv lift.
So far on initial teardown I found a seal that was starting to leak so at minimum I can replace that seal even if I don't find the real problem and have a small sense of accomplishment.