Although there are certainly a lot of disreputable dealers on eBay, there are also sellers who legitimately just don't know what they're selling. One of my best eBay purchases was of a Tamron 24mm lens with a blurry listing picture and a confusing description. I don't recall if the seller claimed not to know much about cameras, but it was obvious that the seller didn't know much about that particular lens. I got it for a very low price and it was flawless.