Amazon started as a bookstore, then after a brief period of being a patent troll it became an generic Internet shop, now it seems to be turning more and more into a shopping search engine, with thousands of sellers using it as an intermediary between themselves and the customers. I'd really enjoy the fight for shopping search engines between Amazon-style thick intermediaries and Google Products-style thin intermediaries. For now I must say Amazon is much more useful than Google Products, but maybe some day with some open standard shopping metadata the fight will be more even.
And just like every search engine Amazon starts to see the problem of black hat search engine optimization. Some time ago I was looking for earphones extension cord on Amazon, and the first results was one by Belkin with cost of £0.01. That's a pretty good price except there was a shipping cost of £4.50 per item, so they were basically abusing the search results screen.
Right now it seems Belkin isn't doing this anymore. I guess someone at Amazon noticed the abuse and wrist slapped them. Amazon as a thick intermediary has plenty of power over the sellers to control abusive behavior. It would be much more difficult for Google Products to enforce good behavior. Here's my prediction:
If thin intermediaries for shopping like Google Products ever become widespread, abusing behavior like hiding shipping costs, transaction costs, taxes and other fees will become as common as it is now in the airline industry.