I don't think there is anything wrong with someone hiring people as a favor or someone selecting a specific vendor as a favor. As long as the company's owner knows what's going on and is ok with it. And as far as kickbacks go or repaying those favors, if it's money, that's taxable. If it's more favors, well that's merely bartering.

When it comes to stock manipulation, I think that's a crime. But if not, I can't see it being profitable. It would most likely result in a net loss unless there was some inside information being shared.