The pulley hides the rotor. If the rotor is stuck to the pulley properly and you feel it slip into position, great. Sometimes it's loose and the tech might not realize it. In my case I could see a sliver of bent metal on one side of the hole when I pulled it to inspect the HES.
Yeah, a conscientious tech will feel it go together right. But once it's done, it's not a very intuitive thing to check. I remember thinking that I lucked out in a big way finding it.
I'm not making excuses for anyone, though, and I don't think a shop should be paid for work that doesn't reasonably contribute to a solution. If it needed a HES, so be it. If the tech screwed it up at that point and never found the problem, well, that part wouldn't be billable here and I'd probably be eating some trailer time. But that sort of situation is rare enough that it should be handled on a case by case basis.