Same with electronics, just stay away from VCRs because scammers buy them and swap out parts then sell on Amazon. I always sell those on FB marketplace. I haven't done any flipping in awhile and have a pretty big death pile at this point. I'm sitting on a few hundred new old stock vacuum tubes that I need to go through and probably do a bulk sale as most of them aren't worth very much. Other than that my most recent sale was a AGP Nvidia quattro card from my personal collection that I sold for nearly $200. Iirc I paid about $30 for it a few years ago before people were really aware of them for vintage builds.

Here's an idea I had while browsing Craigslist for a stationary bike.

People ditch these for nothing or next to nothing and if you Google the model number on the ones with screens, there's a good chance you'll find an eBay/other auction - often with bids - for JUST the screens. And they ain't cheap.

The most expensive bike I saw was $100 and the screens ranged from $100 to $350!

Granted, now you've got a screenless bike you have to deal with...but still, I was quite surprised to see people were buying the screens