It can be hard to tell sometimes. I had a low mileage New Balance boot come apart after some river crossings-the sole came unglued from the upper. Didn't expect that from a brand name shoe. Now I have a pair of NB running shoes I wear all the time and they are fine.

I used to buy Hi-Tec boots for work. They would wear out after a few months of being beat up, but never came apart and they were cheap at the time. Cheap gear will often start to come apart right away, but some people swear by cheap brands and don't see why they should pay $400 for a tent when they can buy one for less than $100. Same for bags.

REI will take back almost anything for any reason, especially defective products, which is one reason to buy from them.

The best way I know is to ask on forums like this one and see if anyone has used the same product. There are fakes online-especially TNF. There is even fake climbing gear like biners, which manufacturers like Petzl warn people not to buy or use so you should buy from reputable dealers and websites. You may pay more, but you are far less likely to get burned.