Chris, I collect coins myself, and would have no objection to a plastic reproduction of a rare coin where I would not be able to afford the real thing.  This would go in my album for illustation purposes, and would be better that just a picture on paper.

I have noticed a lot of coins listed on here, by what I assume to be honest sellers, as Fantasy coins.

Are these the ones you are referring to.

There is a similar problem with stamps such at 1d black etc, there are reproductions on sale, but they are described as Forgeries.