This is kind of a compromise between the first two. If you're generating a lot of traffic, this could add up to be quite a large amount. Different merchants have different ways of tracking your visitors. A popular method is through the use of cookies. Some of the better merchants track your visitors for years which is a good way to make sure you get rewarded appropriately.
Most affiliate programs are very easy to join.
Affiliate programs have become very popular. Even the major search engines pay you money to provide a link to them. To get started, check out the Affiliate program directory or read the Affiliate program reviews .