I know nothing about aircraft avation but I do know that a lot of repair shops around the states follow a simple business practice. Get as much money as you can for the least amount of work. The dealers are even better at this than private shops.
dealers for the most part, charge "book". this means, that for instance, your lexus needs a new steering rack. the book calls for 4.5 hours to do this job. that's what you'll pay in labor, regardless if the tech does the job in 2 hours, the quoted time of 4.5, or even if he takes 6 hours.....they charge you that 4.5.
then you pay for the rack...which, regardless of where they buy it from.....toyota, napa, auto zone, etc, they will mark it up. this markup varies a LOT. then you pay for fluid, and probably an alignment.
then you pay a shop fee, and a hazmat fee.
most private shops(at least in my area) are anywhere from $10 to $50 an hour cheaper on their labor rate than the dealer is.
most private shops will use "book" as an estimate only. that's what i do. on that same steering rack, i'd quote you that 4.5 hours. if it takes me longer, then i lose. if i do it in 2 hours, i adjust the bill accordingly. most shops in my area do the same thing.
we also mark up the parts. there is no way that any of us can or will buy a part for $100, and then sell it to the customer at $100. we'd be out of business in short order.
most of us sell the parts to the customer for "list" or somewhere near list.
this is just like anything you buy.
john makes shirts. he sells them to bob for $1. bob sells them to jim's shirt supply for $2. jims shirt supply sells them to several shirt retailers for $3 each. these retailers sell them to you and me for $6.
take that very same model, and apply it to automotive parts.
when i work on bmw's, mercedes, etc, i often come in significantly lower than the dealer...or so i'm told. i use the same quality parts, my work is either equal to or better than the dealer techs work, and the customer leaves happy.
there are a lot of repair shops out there that are rip-offs. they;re becoming rarer though.