Wow, impressive use of selective quoting to take two completed unrelated arguments out of context. To clarify, "things like that" was a very specific reference to non-working prototypes. I'm not aware of too many situations where a seller of a non-working prototype does anything besides asking potential buyers to make an offer because the seller just assumes the item is pretty worthless and doesn't want to look like a fool setting some unrealistic price for an item that is very hard to sell even in the best of cases. In fact, I have yet to find an example on Assembler or Nintendoage or Atari Age of someone advertising a non-working prototype for sale with anything other than make an offer. As such, you're not going to see lasting price information because the post gets deleted and nobody ever thinks to ask or report what it sold for because few if any people care.
On very expensive items, there is no reason to hide the ball. I'm pretty sure you're one of the guys that is looking to pump prices on Nintendoage and you've been very cagey about what your items finally sold for, no doubt because you're looking to maximize your profit and not because buyers are asking you to protect the pricing information.