I'm often wary of those complaining about Google's policies because they're based on the idea that being listed on Google is a right and not a privilege. This, to me, is faulty logic. Unless they're deliberately taking part in anticompetitive behaviour by blocking competition, I think it's perfectly within their rights to delist or demote you for pretty much any reason they can think of.

I think Google have made it pretty clear that as far as they're concerned they don't want people selling links to other sites in a way designed to manipulate search-engine rankings, and if you do so you may be delisted or have a lowered ranking on their site in the future. I think that's specific enough, personally, and think that anyone wanting a more specific policy either wants to work around them to violate the intended spirit and complain if and when Google punishes them for doing so.