I charge an average market rate; some people may be cheaper, some may be costler. When it comes to fault finding specifically, some have complained in the past about my charging a full-hour because I found the fault "too quickly". For that type of job, what you're being charged for is the desired outcome and not the physical minutes spent on site. If I happen to get to where you want using my specialist tools and expertise quicker than some fat slob who doesn't know his asshole from his earhole, then that doesn't make my service somehow worse value for money. So I'm not prepared to be penalised just for getting the job you wanted doing... done efficiently.
For any work, if I'm supplying materials, there will be a mark-up on those materials. The mark-up increases according to the risk of a warranty call, because failures happen. I'm not insterested in anyone thrusting a catalogue under my nose to show a cheaper price than what subsequently appears on my invoice. My mark-up covers me selecting the right goods, ordering them in, collecting them, transporting them to site and taking on responsibility for the warranty. All of that does not come out of my labour charge which is for my time and expertise on the job, not all the overheads before I begin! If you want to trundle off and source all the parts for yourself to save paying my mark-up, you go right ahead. Of course, it's not my warranty then, so you'll have to sort out any failures or returns yourself. Also, my trade suppliers tend to punt better quality goods and not everything is made equal.
One last thing: the business may bear my name, but the money doesn't go directly into my pocket to be blown on cigars, booze, strippers and hookers, and there are all sorts of tedious overheads the company has to cover just to keep afloat. I'll always make sure the invoicing is a fair reflection for the goods and services received, but with the labour costs listed here up-front, I may not be sympathetic to complaints after the fact. Don't like the numbers above? Well, shop around!