This happens quite regularly in the automotive world:
“Hello this is Bob. I had my truck in for alignment last week and you found worn ball joints and tie rods. When can I get those fixed?”
“We can get you in Tues at 10. Let me look up your history here…looks like we quoted you $1150 and no charge to recheck the alignment.”
“Yeah but I have all the parts you listed so it will just be the $680 labor right?”
“No sir, we don’t do repairs with customer supplied parts. We’ll do the job but with our parts for $1150.”
“Well I bought the parts from Amazon for less than half what you’re charging me!”
“OK, did Amazon quote you a price to install them?” Etc, etc, etc.
Now we will occasionally make exceptions. When I had my own place I had a customer with a 62 Bentley. It was a “wedding car”, people would hire him to drive for their weddings, prom, etc. One day the car was in and needed some brake parts. He said he had the parts we needed, brand new, at home. I gave him my shop truck keys to go get them.