You can always install the OS X release that your Mac came with. If that was Yosemite, then all you have to do is boot into Internet Recovery and download it from Apple directly.
See here:
https://support.apple.com/HT201314.
It just means that Apple is seemingly not going after sellers who do so, but it is likely a copyright violation nonetheless. When you buy it from them, you never actually obtain a valid licence from Apple to run it. You are only allowed to run the software that came with your Mac or the software that Apple licences to you elsewhere, which is nowadays almost always the App Store.
Mkay, yeah I can see where you're going with that. But it came with whatever OS X was around late 2011, and while you can update to newer OS X versions you purchased in the Mac App Store, that option doesn't include the versions that came as casual updates. And I'm a little concerned about reverting to a platform that old, if I don't have the option to update it to Yosemite. Thank you though!
And fair enough, I guess I wouldn't have used the phrase "copyright violation" unless someone was going to get into trouble or run into copyright related snags later.
That absolutely is a copyright violation. Apple didn't grant the eBay seller a license to distribute OS X that way. That said, it is free, so Apple is unlikely to aggressively pursue someone doing this.
Do you not have Yosemite available in your "Purchases" section of the App Store? If you've downloaded it from the App Store before, you can easily do so again, and create your own USB installer. Alternatively, if you have an Apple Store local to you, you can likely bring a USB drive there and get them to give you a copy of the Yosemite installer and avoid paying someone extra, and be assured you aren't getting any sort of malware.
Well, technically, I suppose. I meant it more as in I doubt Amazon would allow anything obviously illegal, and if Amazon will allow that to be sold and purchased on its site, then I'm sure there are no repercussions for seller or buyer. After that, it's up to our individual consciences to struggle over whether or not we can live with ourselves in light of our actions. I can do that.
No, Yosemite came as an update. So that option is out. But I like your idea of going to the Apple Store though. I'll check into it, thanks chrfr!