My question is: Do you really need to ask that? Human nature is human nature; there's little doubt that it's happening to some extent. Virtually impossible that it's not happening at all.
The problem to me seems quite similar to campaign contributions in politics. Yes, it's indirect, and all parties can say it's innocent, no strings attached, the elected representative is not "required" to do anything. Those are words that help people ignore the reality of human nature. Money is influence.