It is said that after the Florida update in 2004, affiliate sites were severely downgraded by Google. I wonder if this is generally true and if so, what is the mechanism. Is Google looking out for links to affiliate networks such as Clickbank, CJ, and Linkshare. It has also been suggested that you should not put Adsense Ads on sites that are of dubious quality as this gives Google an extra avenue to catch you.
I thought that the problem with affiliate sites was the duplicate content (if you do not change the product descriptions they are the same on hundreds or thousands of other sites) If however you rewrite the descriptions and make the content unique then I do not think Google cares what you are selling and you will not get penalised.
On the other hand if the case is that they understand the affiliate sites from the links (which I don't think can be true) you can allways use your own redirection system with rel="nofollow" links.
A very well-known SEO expert thinks it does happen although he is not 100% certain. His reasoning is this 1. This is something which Google wants to do in order to reduce clutter 2. It would be very easy and cheap for Google to use a database of domains from affiliate networks or affiliate providers -Derek
That's very true. Another problem with affiliate sites is that they are not accepted by directories (at least I don't accept them in mine, and I know that many directories do the same)