Aircraft components must be manufactured with a controlled quality program and documentation. If a part is installed that is not certified and the FAA finds it, the aircraft is grounded. If it was installed by a certified mechanic, he loses his certification.
This is true, but it ignores the issue of "is the part different". In a lot of cases, no, it's not. It's exactly the same part, just one that's passed certification, that cost 25X as much.
The one I'm surprised nobody mentioned yet is boats. "Marine grade" parts are just nuts. Go to your local West Marine and take a look at some parts you might use on a tractor, you'll feel great about the prices you're paying for tractor parts. And the same situation exists there, I'll never forget buying heat shrink ring connectors there, it was like 25 bucks for 5 of them. Found the same connectors on Amazon or Ebay for 25 bucks for 100! The markup in local stores can be eye watering, I'd never go to West Marine unless I was in dire need. Also, as I got more and more familiar with my boat, I started to swap in a lot of "non-marine" parts (typically GM) and found them to be identical to the marine versions. There just isn't much/any difference, not to justify the 3-5X increase in price. OK, even if this Mercruiser valve is better than the GM version, I can buy 8 of the GM versions and have 7 spares. Pretty sure I'm gonna come out ahead on that deal.
One of the craziest ones for me, my buddy had a go fast boat that needed a prop. IIRC, the total price rang in close to 10K. Yes, it's a chunk of brass that's been though a CNC machine. But 10K? Come on, you can't tell me that prop lives a harder life than the track on an excavator, or any other heavy equipment part! The price inflation is just insane, I'd be shocked to find that prop costs 1K in materials/machining.
