I've seen a lot of articles and posts about artist's work being stolen and used/sold. There was a facebook page that was just selling stolen art printed posters or on T-shirts. A lot of people reported it and it still didnt get taken down for a few more months.
On the other hand with his art style i think there's several industries that could definitely be somewhere he can go to
- Trading card Games
- Board Games
- Video Games
I think he can probably start posting more of his art at more places to get some attention and maybe start up a patreon account.
This is what I've told him as well, he agrees and is getting some portfolio work together, but I'm telling him all of his art has a market as his skill level is obviously very high and has a unique look and feel.