Any and all of the pricing data is submitted by the sellers. If a seller chooses to make the final sale price public (especially in a OBO ad), they have the option to do so.

The sales fee is based on a pre-established tier-based system that pretty much matches what a game is considered (A-list, B-list, C-list, etc). It is not percentage-based of a specific price in an ad. So, even if the market price of a game fluctuates, the tier that a particular game is in doesn't actually change and the sales fee remains the same.

For example, if someone is selling a HEP restored game at quadruple the price of a typical example, the game still remains in the same tier and has the same sales fee for that given title.

There are standardized fees in place. They are based on the game title, rather than a percentage of a dollar amount in a listing price.

I have no idea what you're talking about here.