It depends.

For things like RAM and CF cards, I've bought them via lots. They don't take up much space and having a bunch of those types of items on hand is useful when doing multiple builds.

For most other hardware, I prefer to buy individually as I am usually buying them for specific builds. I also don't mind paying a bit more if it's an item that has been confirmed working. It saves me from having to troubleshoot and repair things.

If I spot something interesting in a lot I'll get the lot as a whole since it's less hassle. Then go through the parts I don't want and recycle them, or keep them for selling on later.
This scattershot approach has lead to me having a couple of boxes full of parts I don't want or just want to use for components, like stealing capacitors and other parts off them and I do have to go through those pretty often to clear out the less useful stuff.

More than a couple of times, a scrap lot I've purchased has ended up containing a lot more interesting stuff than was visible in the pictures, so it's like a physical loot box in a sense.
That's not going to work for everyone though, I'm in this hobby more because I like fixing things than using them it seems.

I rarely visit eBay for electronics these days. However, when I buy gadgets locally, the seller will sometimes sense my electronical nerdiness and say something to the effect of "Yo dawg, I've got more stuff in my attic/basement/closet/fridge I think you'll dig. Wanna check it out?"

And I'd think to myself don't say yes, don't say yes, don't say yes. Then blurt out "Oh ma gad, totally!!"

6 out of 10 times, it'd be something overwhelmingly great that I wouldn't want to live without. So in some strange freak of synchronicity I'd come home not only with a computer monitor, but also an extra power supply, integrated amp, 8 LPs, and an area rug Woz would be proud to have.