Issue #1) Google and other search engine specifically state that selling links to manipulate rankings is against their guidelines. I'd be wary against associating my sites with purchases from anyone who is buying links.
Issue #2) If this is worth the financial cost to another, why aren't you personally taking advantage of the extra link(s) to promote your own sites. In the long run, if done right, you can make much more money directly than anyone would ever pay you for the links.
Jason, my comments aren't to dissuade you but instead to give you another perspective of thought. I remember having the same sort of mindset when the idea of paid links came out, then it was paid blog reviews. We know what has transpired with those tactics. I believe in the long run a similar scenario would occur (eventually).
My advice, leverage your resources for yourself while staying within the guidelines of the search engines. You'll sleep better ... and get richer quicker
