Earlier quoted context omitted.
Interesting idea, but I seriously doubt Amazon would do this with their normal warehouses -- maybe paying sales tax and thus being able to have presence in major cities would let them set up dedicated showrooms for certain kinds of high-lifetime-margin products, like Kindles and maybe a Kindle Phone, though. Big warehouses are highly automated (especially Amazon's), essentially unsafe for untrained people (forklifts,…
If Amazon can deliver in one-day, why even worry about stock at these showrooms. Find something you like, order it, and it's delivered to your door the next day.
Also, many people feel "bad" about buying and returning. The "buy 3 pair of shoes, return 2" where you know you'll only keep 1 from the start feels dishonest in a way, although I'm more than happy to return something which isn't as described or is otherwise unpredictably unsatisfying.
I actually do a mental calculation before buying something which I might return, trying to figure out if Amazon is better off by me buying it (given my odds of returning it, and the costs/residual resale value if returned), and if the return is due to a bad description (Amazon's fault, and thus ok to return if the product turns out to match the wrong part of the description, like when it is internally inconsistent with the photo or whatever).
"Which of these two should I buy" is sometimes addressed by buying both, but buying 10 items and returning 9 is probably going to get your Amazon account flagged at some point.