> our data show that people usually prefer links that take them directly to the products they want, not to websites where they have to repeat their searches.
If you would link them correctly, there wouldn't need to search again, but would be on the search results of that other site with their (usually better) results.
Also, considering that product search results are sponsored, usually the top results at product search are crap. There are three things that people usually prefer links to when they search for a product:
1. High quality product information - that's usually the website of the manufacturer. Amazon is not too bad in some cases but smaller retailers usually lack a lot of useful information.
2. Best offer - when you pay for being a top result on Google product search, then it's hard to claim you will be able to provide the best price.
3. Buyers feedback - sites that are larger usually have more prior buyers and thus more feedback. Google's very own ratings (which the scrape from other sites that allow them I guess) is usually crap compared to what you find on Amazon.
So basically, if Google would want to provide actual useful search results, this would just be a link to the manufacturers marketing site, a link to the best offer and/or the result page of a price-comparison site, and a link to Amazon and/or comparably large local retailers. Results based on who payed most is not what people usually want, don't try to argue that this is true.