there is nothing wrong with the offer. except that it's based on trusts. how do you know he will give you 15% back.
I have seen so many offer like this, the guy offer to teach you how and what to upload an where to post etc. and in return he give percentage of what you make for him.
but do they pay, who knows. if you are not registered on fileserve already and he offers good tips, even if he doesn't you don't lose anything.