Sounds like a good idea to me. A shop specializing in survival, preparedness, and camping gear that has been pre-owned and/or lightly used. Sold at a discount or a nominal cost.

I am notoriously frugal and tend to use, reuse and patch gear until it is useful only as compost. I have gear that is thirty years old and, although patched and not quite as pretty as it once was, it still works. Even if it has been demoted to less stressful jobs. Stuff I used to use to hike with, now carries lunch. It also means I rarely buy new gear and tend to be a little skeptical of the claims that this or that new product is a substantial improvement over what has been around a long time.

That said I have pensioned off gear to friends and family of friends and generally like the idea of recycling and reusing it. I also think that people getting into preparedness or camping is a generally good thing. If the availability of reduced price but reliable gear gets more people involved so much the better.

Setting up an exchange or store specializing in used gear might be made easier because a lot of people tend to go through cycles of heavy then lighter emphasis on equipment. I know people who have started with borrowed camping gear. Went on to get deeply involved for a few years and spend thousands of dollars on new gear and then, for various reasons, found they only actively used a small fraction of what they bought.

Lots of people find that after a time they settle on a few favorite pieces and the remainder, often enough to equip several people, just acts as closet filler. No reason this excess shouldn't be sold and reused.

Your idea for an e-store sounds like a grand idea.