Concept art royalty question

Just wondering if anybody has any advice on how much a fair royalty percentage is for an artist doing concept art for an indie game.
Or maybe an average of what other people have gotten? Thanks for any input.

Kind of depends on how involved they are.
If they just help come up with mood/look images early on, and then leave the project, a fixed payment may be better.
If they are integral to the development of the game, helping clarify different game concepts before development, and help or serve as art director, they need a sufficiently higher percentage (full share if you just split evenly across contributors.)

Most professional freelance artists avoid royalty payments. Unless you are partnering with someone, royalties scare away good artists.

Most professionals will require money up front since a royalty in the majority of cases means they won’t get paid if/when the project doesn’t turn a profit. It’s unlikely you’ll get anyone experienced to work on it on just the promise of royalties unless they really like the concept of the game.