Affiliate Programs
For a long time, a perfectly valid method of promoting one’s site was through the creation of affiliate programs. There are many varieties floating around, but the crux of the concept is that you are offering a reward to others to place your link on their site. This is, of course, a mutually beneficial relationship between you and the link sharer, but the search engines frown upon it because it is yet another way of gaming the system. When a website without quality content can buy its way to the top, algorithms must be changed to accommodate.
Nowadays, large indices such as Google no longer acknowledge affiliate links by refusing to acknowledge any link with extra variables in the URL string. For example, a link to http://www.somedomain.com would be fine. However, a link to http://www.somedomain.com/?affiliate=name would not. This is because most affiliate programs rely heavily upon these extra variables to track their affiliates’ activities. Of course, the links may still produce conversions, and they can still be tracked by server referral, but they lend nothing to link authority or theme.
Thus, tracking affiliate links can become tricky business, if you care to do it at all. Most search engine marketers consider this tactic neither black hat nor white hat, falling in that grey area where search engines are grumbling but not overtly complaining. After all, the links are being placed on legitimate websites by willing webmasters. The only question is what compelled them to do so, which is difficult for a search engine to determine. Let each search engine marketer exploit this fact or not according to his/her own degree of professional ethics.