I thought I read something about that you weren't allowed to have competing ads, like if I had Adsense ads for mobile phones and then sold private advertising to advertisers advertising mobile phones. It doesn't seem to make sense though, did I read that wrong?
You can have other advertisements, what you shouldn't have is an advertisement that looks like adsense or claims to be adsense, but is not.
Well, Google only considers the appearance of the ads, not the nature of content. You can have other ads about mobile phones, but you can't have the racing car ads that looks similar to the existing Adsense ads.