Something to watch out for: sellers who want you to believe that they sell high end mobile phones (so that you are more likely to buy the information that they are selling), but who don't in fact sell mobile phones.
This is the trick: the seller appears to have mobile phone auctions, but he always sets his reserve price so high that there is no chance of him ever actually selling any phones. If you look at his feedback you will see that no-one has ever bought any phones from him, just information about where to obtain phones at supposedly wholesale prices.
The seller poses as a genuine seller of mobile phones purely to fool you into thinking that the information he is selling is more worthwhile than it actually is. In his listings selling the information he may have the cheek to say things like "And what about the sellers that tell you where to buy mobile phones at wholesale prices – yet they don’t seem to sell any mobile phones themselves? If they could get the phones so cheap, why aren’t THEY selling those phones?" The seller certainly seems to sell mobile phones himself, but remember - he only seems to.
No doubt there are sellers trying to pull this trick in relation to other products as well.