[asr]

Manufacturers often pay stores for space on the end cap. http://www.cockeyed.com/citizen/retail/raleys.php

As far as I know, "Amazon's choice" is not an advertisement/suppliers can't bid to be Amazon's choice.

[ceejayoz]

Not directly, but if it's based on things like purchase volume and reviews, it can certainly be gamed by paid actors.

[dredmorbius]

Shelf-placement generally, via planograms.

https://en.wikipedia.org/wiki/Planogram