Turning down easy money that feels shady is the kind of brave that lets you sleep.

Money that arrives with a bad feeling attached does not come clean later; the feeling is the price and it gets paid in instalments. Saying no is harder when you need it, which is exactly when these offers tend to appear. What you are protecting is not a rule, it is your own account of yourself.

If you cannot explain how it works to someone you respect, that is your answer. Turn it down early, before you are involved enough to be negotiating with yourself. Then go and find the slower version.