(a) used books. As a Midwesterner I love that can directly order specific technology books (the ones everyone recommends), literally from a Goodwill in San Francisco, for the price of a good meal

(b) dodging Amazon co-mingling of inventory. Do I trust Amazon doing whatever it wants in a warehouse, or some eBay seller with a few years of built-up-reputation to lose but who specializes in the part I want? Let me tell you I have gotten a lot more handwritten thank-you-for-your-purchase notes from eBay sellers than Amazon. 3D printer parts, used computers+parts for the homelab, laser printer replacement parts, etc.

(Yes Amazon said they would stop recently... Not sure I believe it's fixed yet)

Not parent, if you want to sell an old original video game you know has value, it's either the proper collector channel (slow, super involved, higher pay), the generic resale channels (fast, no effort, lowest amount possible) or ebay (relatively fast, a bit involved but not too much, pay depends on how good you defined the product).

I had some old stuff around that Mr everyday might find (eg pristine original Gameboy Pokémon cartridge without box), and quick resale would give me 10 euro, involved resale would ask me hours and hours of work ebay allowed me to sale for 120+euro spending 1h on the description and picture (to show the scratch etc).

Another case is "oh you have the msi ge77vx4 laotop and you look for the plastic keyboard map in azerty? You can pay a 500e rma if they even allow it or buy the piece for 20e on ebay and fix it yourself"

Ymmv but it has a specific place that no one really have right now

I use it for non collectible stuff. I’m always buying weird interesting things. Old computer stuff at least once a month.

I buy most of my physical games from eBay too

I was selling NES/SNES games + boxes. After ~2 years of sporadic sales, I ended up just offloading them to a guy who has a huge used games outpost at a flea market.

I buy a mix of things: clothes, watches, and usually tiles from my favorite pottery in Michigan: Pewabic.

Literally anything that isn't actively manufactured anymore. Even a lot of specialty stores will just sell through their ebay account.

It's great for used car parts (both buying and selling, as a hobbyist)

I use them to buy refurbished enterprise machines -- laptops & mini PCs, books and DVDs/BluRays. Works pretty well actually, never had any issues with the quality as long as you stick to reputed sellers.

I frequently buy project car stuff on Ebay. You can find OE stuff with the part numbers scratched off that must have "fallen off the assembly line" pretty easily. Easily a few items per month between that and computer parts!

I'm the same way as OP. I'll go clean out my basement, find a load of old tech and just put it up in a bundle or sell it individually for dirt cheap. Likewise, I buy a lot of stuff like minimal wallets, micro-electronics like charging cables, dongles for my work laptop, phone cases. Just typically a lot of knick knacks or older tech stuff. There's a booming economy for old walkmans and cd players. Same thing with higher end audio stuff like older DAC's, speakers, amps. A lot of unique stuff you can't find on Amazon or elsewhere.

There's a lot of low volume and niche stuff sold by industrial ecommerce (grainger, Mcmaster, etc) and sites specializing in a given niche that those sellers cross list to eBay (the higher volume stuff is typically sold on Amazon)

Probably Pokemon or sports cards.