Here is my take on this, as we all deal with this dilemma everyday one way or another. IMO, your job/responsibility is to provide a service/product at a price that is fair to the customer and to you. In other words make a profit. The manuf./distr. has the same responsibility. Until you see his books you can't be sure if he is ripping you off or not. His overhead/life style/etc might be too high. The bottom line is that if you find what you need at a lower price somewhere else that is not offset by convenience/friendship/time or something else then you buy it where you get the best deal.
I bought a Powerain automatic mainly because there were no distr. closer than 200 miles and 90% of their parts could be bought at a local Grainger. PR sold their parts for 200-300% more than I could get them at Grainger. I urged them to sell "us" the parts at Grainger's list and to be able to pick them up locally. IMO everyone won, they made money. we paid no extra and Grainger made money. It never happened, I guess they are still around, but I haven't heard of anyone buying a machine from them in a long time.
Another reality, a couple of my friends own and operate a Big O tire store. For years I bought my tires from them. The last time, I got a price from Costco and went over to them and they were $25 each tire more. I told them that I was sorry, but I wouldn't pay $25 more to give them the business. He told me that they had to pay more for the tire than Costco was selling them for. I suggested that they get out of the tire biz. A few months later after 10+ years, they gave the store back to corp.
I tell my clients that their reality means nothing, its the customer's perception that is the customer's reality. If their parts are propitiatory and/or they need to charge those prices, and the customer feels screwed it will kill them in the end.