To be fair it definitely happens in a huge variety of industries.

That doesn't make it too much less sleazy though. And your analogies are not on point, those are ordinary markups--your markup is more like the guys who put your tire on charging a $10 "disposal fee" for tossing your tire in their dumpster when they're done.  They make a profit on that, it doesn't represent the value of the work, and the profit is disguised from the customer in the form of what appears to be a passed through fee.  And you know, sir, when you go to get your tires changed--how do you feel about that fee?  Do you have them do the disposal?