Second hand marketplace for dogs

Personally I don't think it's something I would use since I find most dog toys and items are relatively inexpensive (at least the ones I buy) with the exception of items like food.

Have you tried asking any communities that are dog or pet focused?

Can you define the audience for this? Bonus question: can you define the most niche sub-audience within "people who own dogs" that you think, among all of them, has the MOST desire to pay for used dog-related items?

I have 4 dogs. I rarely buy second hand things for them. I once bought a second hand crate. I looked for harnesses once but I went for new. Not sure I would’ve bought one even if I found used due to possible diseases, hard to find correct size and type even if new, etc. I’d never buy toys second hand - they don’t have a long life anyway and half-chewed things won’t be worth any money.

Also it’s hard to beat Facebook marketplace or Gumtree for local random second hand things. Non dog related I use these a things a lot. As with any marketplaces it’s a chicken and egg problem and I find these hard to beat, especially Facebook they made it too convenient and easy.

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https://shepskymix.com/german-shepherd-husky-mix-puppy/

its pretty impressive to see this bcz i latterly working on the dog braces project for my second blog you can see the link and take some guidance about it see here https://dogbraces.net/

I thought at first you meant a marketplace for selling your dog lol. But yeah, I agree with @johncb , ask your target audience, maybe via Reddit or Facebook groups with dog owners.