Was I surprised to see a poor review on Bodybuilding.com! I've ordered from them for a few years now, regularly, and liken them to the Zappos of the fitness/health world. Fast shipping, extraordinary communication and customer service, excellent pricing. I have never had anything but ideal customer service from bodybuilding.com.
While I found it fairly easy to set up to SELL on amazon, the company doesn't offer much support to their sellers. Additionally they make the feedback system somewhat unwieldy - I was left bad feedback from a New Jersey seller THREE DAYS after a purchase because she did not yet have her product (and was subsequently suspended by amazon from selling). For some reason amazon makes it difficult for a buyer to contact a seller. I've also heard countless tales of amazon engaging in the practice of "holding" sellers' funds... to the tune of thousands. Considering how they treat their sellers, I have really limited my amazon purchases.
Amazon hardly makes it worth your while to affiliate with them. They're incredibly cheap about commissions and hold your funds for quite awhile. On the plus side, they make doing affiliate business very easy and their banners, links, etc. are easy for a novice.
I admit that, upon visiting the site, I was intrigued. But then I read the comments here. It's a shame that, given this dude's obvious knowledge of programming, that he couldn't come up with a valid alternative to ebay. I adored ebay years ago but rarely frequent it anymore. My 100's of favorited sellers have all disappeared (you note that ebay never releases stats on sellers) and a huge percentage of the sellers remaining are overseas. If someone started a site comparable to the ebay of 10 years ago - pre-Whitman - they could do very well.