It's sad to hear that someone is trying to make money off of someone elses work. I always ask the individual responsible (if they are contactable) before using their code/art and I certainly wouldn't use anyone elses code/art in sellable stuff without a proper legal agreement in place.
I don't know Cosmos and I don't think I have used/seen any of his stuff. I hope he continues to work on his Amiga projects.
Any of us releasing games/software for the Amiga (or any computer/console) are potentially subject to the same thing (someone claiming our work as their own) and it sucks.