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The problem with Amazon is that it is a race to the Absolute lowest possible price point. Now don't get me wrong, I'm not saying that boatloads of vendors don't make money advertising there (and people on Amazon are for Sure in the market), but wouldn't you rather get people to your own website via say YouTube, which is only going to get more and more popular, and then convince them to buy from you Now... I would if…
Problem is it's much harder to get sales elsewhere. On Amazon, you can sell a $25 item and maybe spend $5-10 in ads per sale. On your own site, you might pay $25 per sale, which means you need a compelling offer at $70+ or so. This is because conversion is worse and bids are only going up as people get better funnels and can afford to throw a ton of cash on ads.
How about AdWords; can Amazon get 50 bucks a click on a search? Nope they can't, but Google does. I don't see Amazon dethroning Google anytime soon for ad revenue. They could, but I think they'd need a high end site that caters to quality and not peeps looking to save $1.96 on a set of Tupperware.