This whole thing has come up often enough and I have just decided that, if other people choose to handle their immigration procedures through an agent, that is up-to-them.
Personally, although I am not suggesting that it would apply here, as an American there is the Foreign Corrupt Practices Act and that is how choose to look at things:
U.S. Foreign Corrupt Practices Act. FCPA makes it unlawful for a U.S. person or company to offer, pay, or promise to pay money to any foreign official for the purpose of obtaining or retaining business
https://www.trade.gov/us-foreign-corrupt-practices-act