There's a big difference between private trading of already-issued shares and purchasing newly-issued shares. With the former, you know it's not going back into the company. With the later, the presumption should be that the money is being used to grow the business.

Nearly every investment agreement has a "how will this money be used?" section, and I can't believe a fund would give hundreds of millions of dollars to a company that was explicitly going to be put it to founders' pockets, unless they too are in on the scheme and are hoping for a quick flip.