Kickbacks

I'd say they're both - illegal and federally prohibited (unless you live in Mexico).

Probably illegal there too, so you end up having to do it, and subject to arrest at the same time.

It is really hard to imagine a kickback without someone being defrauded.

Hmmm......................I know that some companies pay supermarkets for better placement of their products. Could not that be considered a form of kickback?
And is that illegal?

I didn't think of that. Maybe they get away with it by calling it promotion or even shelf charge, or something. It is certainly common practice, and common knowledge. Anyhow, if it is between the store and the vendor, there wouldn't be that element of fraud.