Yeah, honestly, if it becomes enough of an issue, maybe eBay and similar should create separate sections for machines with memory and those without. I mean, there are reasons people would want to get a system without memory too, especially if one's looking for other parts, but I do totally get that it's super-obnoxious if there isn't a way to filter those out and one is looking for one with memory.

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It doesn't look like eBay has a "0 GB" memory category, annoyingly enough, but they do have a "Not specified" category with a ton of listings. That's not absolutely the same thing, since if you filter "Not specified" out, I'm sure that it might also exclude some listings that have an unknown amount of memory, but I'd guess that that'd get you most of the way there, and I do see people clearly listing machines with no memory in that category.

EDIT: Honestly, the rate of mis-classified listings there by users is pretty bad, even aside from eBay not providing a "0 GB" category. I was very surprised to see that there were a bunch of 512 GB listings. Looks like that's essentially all people selling machines with 512 GB SSDs and choosing the wrong option.