Because Rep system can easily be abused and is freely available to anyone. Most people (including myself) have rep for some rather useless things... It would come down to a popularity contest... And its not monitored as closely as spamming for posts, which a member can report but cannot change the post.. With rep, if you don't like someone, or disagree you can neg rep the hell out of them and they'll what, lose access? Seems unfair, thats why are aren't ALL mods. I can see it causing more problems that its worth
I don't think users should go up a rank for donating, but I think you should get a donator userbar/rank like you would for winning or leading a giveway, contributing, being an expert trader, etc.
think a gd rule would be for level 2 and up can sell for usd, any ranks below can only sell for np, if they want they can buy using usd
I like how they have that worked out right now, because you have to gain trust to sell here. So there are less scammers.
Why not have a time limit aswell as well as post? Say 3 months for level 2, 6 months for level 3 etc... Apart from what's mention I can't think of any other ideas