Unfortunately and sadly, NIB can mean:

New In Box
Not In Box
Never In Brooklyn
Nathan Is Barfing
Nancy Is Baffled
Nothing is Bad
Nothing Is Believable...

... or anything the seller wants it to mean, UNLESS the seller clearly defines the meaning of the acronym within an ad or on the same site.

Caveat Emptor was true in ancient Rome, and still is. Buyer beware! Trust, but verify.

The sting of poor quality lives on long after the pleasure of paying a low price. That's why I buy used goods from KEH.com and MPB.com, and new or used goods from B&H, or Adorama, or a local camera store if there is one (nearest is 76 miles from my house). All of them — with the exception of some local stores — offer either the US importer's warranty, or an in-house used goods warranty. I may pay a bit more, but I get what I pay for. I trust the four dealers I mentioned. I've always been pleased with their performance

The few times I've used eBay, I've checked seller ratings, seller experience, feedback reports, and anything the seller detailed about the item. I once had an opportunity to buy a used lens for a third of its current list price. The guy who was selling it had a low rating, with few sales. As soon as I saw that, I moved on.