I've purchased most of my beginner backpacking gear from a used gear sale. The reasons people return things can be interesting or downright funny. Here are the big items I've purchased from an REI used gear sale:

Thermarest sleeping pad (reason returned: not long enough)

REI Halo +25 Sleeping bag (reason returned: too warm)

Extra jetboil cup (reason returned: didn't use enough)

Black Diamond poles (reason returned: customer found cumbersome)

Down booties (reason returned: not warm enough)

Patagonia puffy jacket (reason returned: down feathers coming out)

I've had zero issues with anything I've purchased and am happy to a) save money and b) pick up something I normally wouldn't at full price (down booties or the extra jetboil cup)