Tanis Ka: You'd like to become a fortune teller?
Player: Yes. Would you be able to tell me how to go about it? Tanis Ka: Easy. All you need is money and luck. Give me 30 gold. We'll play a game of dice. If your luck is better than mine, I'll acknowledge you as a fortune teller. Player: 30 Gold? That's it? Sure, why not.
Selecting "30 Gold? No way!" will fail and remove the quest from your quest log. It will also use up the Mystic Scroll. Since he doesn't actually take the 30 Gold, it's safe to continue.
