I've recently heard of an artist who is selling prints that contains other people's characters. The art and style is her own, and the art with characters are either gifts or commissions. The prints for sale include the original piece uploaded to art sites, without any recoloring or hiding others' characters. Should people buy these prints, it's basically making money off of others' designs, right?
It's not okay, right? Is it legal? Rude? Or just frowned upon?
How should someone handle this kind of situation if the artist in question is a friend?
Any advice, A_B?
Edit: Thanks everyone for your very useful replies! :)