It doesn't make sense to make your affiliate links rank. Google may remove them sooner or later (sooner in my humble opinion).

It makes total sense if you think about it. Google and other engines index URLs, NOT web pages. There is a difference...

While example.com/some-page/ and example.com/some-page/?aff=18188 might render the same page, the search engines treat them as separate pages in their index.

As such, if affiliate 18188 goes around and drops his/her affiliate link on thousands of sites on the web, the search engines are going to see thousands of inbound links from other sites pointing to the page in their index whose URL is example.com/some-page/?aff=18188.

The web site owner who actually owns example.com/some-page/ might not have built any external links to that page.

So in this example example.com/some-page/?aff=18188 will likely outrank example.com/some-page/ for that page's targeted keyword phrase. What is unfortunate is that everytime someone clicks on that affiliate link in the SERPs and buys a product, that affiliate is going to get credit for it simply because the web site owner didn't take the time to promote his own URLs.

If the owner of the site where smart then anytime someone requested example.com/some-page/?aff=XXXXX they would store the value of the aff= query string parameter in a cookie (or some type of session variable), remove the aff= query string and associated value from the URL, and 301 redirect to the clean URL example.com/some-page/. This way the web site owner's page would get credit for all of those inbound links from all of its affiliates (at least those links that are FOLLOWed links).

Then the web site owner's URL (example.com/some-page/) would be what shows up in the SERPs and they wouldn't have to pay affiliates unless they drove traffic directly from their affiliate sites.

This is one of the best techniques with regards to page ranking as long as the content is high quality and related to its connection there is no doubt for that rankings.