Of course I'm not trying to defend sleazy sellers. Let's put it this way: A seller lists a recessed igniton from a K0 and list it as "sandcast". Well, the ignition didn't come from a K0 but will definitely fit a sandcast, so he is not lying from my point of view.
Now, another seller (as I see lately) lists a CB350 chainguard as "sandcast", while there was no sandcast CB350, at least that I know. What does the "sandcast" mean? Nothing, he is just trying to get more hits, but nobody restoring a sandcast will buy his chainguard, nor will I pay more for it. Like those sellers that list "CB750 Not kawasaki Z1 ", they list a CB750 and will get the attention of people looking for a Z1. He is not fooling anyone, but chances are that somebody looking for a Z1 ends up buying a CB750 if it is good looking.
Regardin the RD350, I bet they clearly state in the item description that the part belongs to a bike that is not a CB350. Then you have the "may fit other models and years". For example, when I broke my CB750 latch I was unable to buy another on eBay, always being outbid. When I knew the CB350 had the very same latch I was able to buy a complete gas cap with latch for about 30 euro shipping included. The intelligent approach from a seller would be to list it as CB750 CB500 CB350 C400, and in the article description, say: "removed from a CB350; may fit other models and years". If you are looking for a CB750 latch, you get a hit on the search engine. Once you open the item description you maybe will see that the item is exactly as yours and maybe buy it.
What I mean is that if you beware no matter what the sellers say. There are lots of auctions for fake garments, like Polo or Carolina Herrera or Dior. They don't say in the auction that they are fake -it is against eBay policies-, it's something the buyer must know beforehand. How do you know when one is the real McCoy? Surprisingly, the real ones must show proof of authenticity, so assume everything iis fake unless proved otherwise.
Raul