Cards that are designed to go into the Market deck, and cards in each Starter deck all have the same back.
Cards that don't go into any deck (like Hero cards, and Hero Ability cards) I believe are double-sided. Same for scorecards.
I'd say that, no matter your experience with Hero Realms, that at least 95% of your cards will have the Hero Realms logo back.
Director of Organized Play
White Wizard Games
Great answer! Thanks a lot!