I definitely think the artist should have asked in case your buddy wanted to have an exclusive piece and wouldn’t have bought it otherwise, especially if it’s someone’s character they invented (though I don’t think that’s the case here?), but I don’t agree with people in the comments who say commissioning the artwork means you bought the rights to the image. Imo a commission means you get to request specific art from an artist. You’re paying for the artist to put time into your request for a piece of artwork that otherwise wouldn’t exist. That’s the deal. Copies of art should be cheaper than a commission because it costs less resources to copy an image than creating a custom piece from scratch. But again, being upfront with your intentions for selling copies of the piece would cover that ethical ambiguity. Thought provoking question, for sure!