[motion]

People will judge the expense/overhead of your operation and self-determine an appropriate level of markup on parts that they will let you get away with. That's just simple human nature. If a weekend hack is working under a carport, well then most people are not going to be comfortable with much of a markup. If a multi-line dealership is doing the work, then people know that they're going to be paying retail+ for the parts.

If they trust you and have been using you for years, then those dynamics probably don't apply.

With so much info at everyone's fingertips, I can see where you're in a really tough spot.

Back in the late 90's, before online internet parts shopping was a thing, I had a Range Rover that ate all of its CV joints and collateral parts. The local shop wanted something like $5,000 for parts to repair. I got on the phone with a Rover dealer in the UK and had everything shipped to me for around $1,500. Hired an independent guy to install everything.