All well said. We're not in this to stab each other in the back. I guess the saying applies to parts as well as complete watches: "Buy the seller, not the part".
There's a bit of a disconnect with genuine vintage parts, however. I don't think anyone here would spend big money on gen vintage crystals, but on TZ and VRF there are lots of people with more money than brains, and they'll pay a lot for the "correct" part. Add in the unavailability factor, and insanity creeps in.
Example: you can buy a CWP bezel for $300 and the gen piece goes as high as $2,000
Example: I needed a replacement crystal for my 6536. The part was unavailable on the aftermarket. I wasn't certain which I needed, so I bought two on VRF, a t-16 and t-18. Now I want to sell the t-18. I paid $400 for it, 5 years ago. Any takers? Didn't think so.
Example: WIS collectors will demand a genuine Superdome t-39 for their early 1665. They would be horrified to consider aftermarket, even though those antique crystals are getting fragile in their packaging. I stumbled across a cache of the beasties years ago, and bought 4 as an investment. Other members here bought the rest. Now I'm ready to sell, and how many takers do I see at $400 a pop? None. And that price is only $50 higher than PonyCar350 was selling them for, almost 10 years ago.
When you're talking vintage, it's the wild wild west. Contemporary is a whole 'nother story.