I have aquire a lot of outdoor gear from thrift stores and kijiji. Full climbing gear kits, tents, sleeping bags, snow shoes etc.
For camping gear I usually look for brand names and quality feeling gear. Just because it says northface doesn’t mean it’s good. Actually there is a good chance it is shit so feel it. Check the seems. Do you need waterproof? Are the seems taped? Is there a rip or tear that will cause issues?
Let’s say you find a nice eureka! tent. You pull it apart and it has a small tear on the fly and it missing a pole. Beauty, you can fix all that as long as the price is right. Make sure the fly doesn’t have sun rott and no hole in the base.
Sleeping bags. For these, I usually start with shape. I look for mummy style mainly because that is the shape of my mattress but won’t disregard a square. Hope it has a bag. Not because of packing it but most of the time the temperature information is on that mofo. Check the zipper for functionality and not to gross people out but for bugs as well. My sister got bedbugs while living in Australia in her bag and have always been worried since.
Everything else. Just use your common sense. If you can fix it, it could be a great staple to your pack but only if you can rely on it if it’s important like a compass, stove or bear spray then you best be able to bet your bottom dollar that that shit will pull through in an emergency. Happy camping.