A lawyer would write it, but something like "Investor represents that he is investing his own personal money and not on behalf of another party". If the investor turns out to be a scout, he has to negotiate that term out and you get the chance to understand what's happening.

Representations are great. Anytime you are negotiating a deal, and the other side makes some crucial claim that persuades you to accept the offer (for example, "all of our other partners agreed to this term!"), just insert that claim as a representation of theirs and watch if they squirm.