I buy tools at flea markets, junk stores, tag sales, and estate sales. I clean them up and fix them up if they need it, and sell them on eBay.
I'll never get rich doing it. It's really just for fun, now that I'm retired. And I certainly won't go bragging about it on Youtube. But... every now and then I find something really interesting, from a design or historical point of view.
I was a mechanic back in the late 60s and early 70s. I bought a lot of Snap-on, and some Craftsman for work. The Snap-on stuff was really expensive even then, and the Craftsman was a decent alternative. I broke some of both brands; it was nice to have Sears just give you a new tool. The Snap-on guy usually wasn't so accommodating.
Anyway, when I find the Craftsman stuff that I used back then, it is sort of nostalgic, but a lot of it is really still in good shape.
Take the ratchets from the early 70s - I dismantle all of them, clean them out, and look for damage. The majority of them are just fine, good for another 20 years or so.
That's a lot of the fun for me: finding a tool that was made right here, maybe a little rusty, cleaning it up and giving it a new life. It's also a reaction to the throw-away world we're in now. There was, IMO, a golden age of American tool-making for the first half (or so) of the 20th century, when many companies made tools intended to last a long time. I like to honor that time.
I'll agree that there are some crazy prices on eBay for very ordinary tools. But people buy things for many reasons, and I don't need to know what those reasons are. I might wonder why folks are willing to lay out $80k for a Land Rover or a Mercedes when something half the price will do just as well. But they do. That's life.