I used to work at a auto shop and one time a lady came in wanting an estimate to replace the majority of the exhaust on her car. We didn't do exhaust work so the only way for me to price that out for her was to go based off the purchase of all the components from the parts shop which would have been way more expensive than a shop that actually does exhaust work. I told her as such and then she insisted that I price it out anyway which took forever because I had to find a diagram of her cars exhaust and cross reference all the parts with the parts shop website and then the entire time she's bitching at me about how long this is taking. I continued to explain that going to an exhaust shop would be cheaper and she continued to insist. When I handed her the estimate she glanced at it, laughed in my face, and stormed out. That shit happened almost 2 decades ago and it still pops into my head frequently.