Memory - "Seller refurbished" vs "reconditioned" vs used?

I’m looking at memory for my FreeNAS build, and I’m confused. I’ve actually been attempting to Google to find the answer here, but it’s clearly not obvious…

When buying (non-new) memory, should I be concerned about the kind of memory I see offered? I have no idea how a seller would “refurbish” or “recondition” memory. Should I always prefer used memory, or does it even matter?