Bob, started this thread since we hijacked the other. You said pretty much everything there is to say about the issue, though, and it's interesting because there is so much gray-area. I agree. I would have a hard time returning something after years of use and complaining that it didn't hold up for as long as I thought it would. Also, there's a balancing act for whether gear fails due to defect of design or user-handling. When sold something that is marketed as sturdy or "bombproof", the burden on the user to exercise reasonable care would seem to go down. (Likewise, if one bought a UL tarp or bivy, it would be much higher.)
You said: "Well, several ways. Read, explore on line, published reviews, get opinions from people you respect, see others using it, inspect it carefully, think and analyze, try it out in controlled settings, ...." And this is certainly true--however, when one goes to REI and pays the higher price and seeks the advice of the sales rep there, one expects to NOT have to do this type of research and instead rely on the information they impart. In a sense, you are paying a little more to not have to spend the time doing market research. So if their advice fails you, perhaps you are entitled to a return. (With regard to my shoes, I tried on numerous pairs, and was sold the most expensive pair I tried on on the advice of the sales rep. I do not have an indoor space big enough to get any reasonable measure of how a shoe will perform on a hike since I live in a tiny little city apartment.)
To me, the most interesting thing about this topic is how it affects UL gear. Does REI's return policy deter them from carrying UL gear that is intended for specialized circumstances and designed to be used with a very high level of care? Probably. (Just imagine the loss on cuben products, if they ever carried them!)
I'm inclined to think their losses aren't that great, though, since the markup on the products they carry is probably somewhat high (compared to the specialized cottage industry products) and they do recoup some of the cost in the used gear sale. Again, I bet the policy pays for itself in attracting customers who would otherwise buy from cheaper online competitors. This doesn't in anyway justify taking advantage of the policy, though, because at some point, if everyone did so, it would become too expensive to maintain and all would suffer.