> . For example, I read a persons blog post who said amazon had a rule that you can't sell your product on amazon and sell it for less on your own site.

I don't know how much of a choice Amazon really has here. Amazon is the ubiquitous online marketplace for everything. If I find your product on amazon, and then later find it for cheaper on your website, I'm not going to visit amazon anymore to purchase said product. You just used amazon as an advertising platform against itself.