In my world, fortune tellers and psychics aren't con men but actually possess supernatural abilities. People born into the Romani lifestyle can make repeated and accurate predictions via tarot cards, palm reading, dowsing, astrology, abacomancy, crystal balls, and other forms of divination. Fortune tellers cannot scry more than one year in the future. A future prediction can also be wrong if a new event occurs (like hearing a fortune) and people change their actions. Of course, there is also a chance that the prediction included other people's predictions and created a self-fulfilling prophecy. Fortune tellers initially use their abilities to great effect on the stock market, casinos, lotteries, sporting events, foreign policy, etc.
So if you are an entrepreneur who runs a lottery or owns a casino, and you're tired of fortune tellers winning all the time, what do you do? Banning fortune tellers wouldn't work because others would simply hire them. You could hire fortune tellers of your own and try to change the predictions but that could create a self-fulfilling prophecy. Random number generation won't make a difference because the fortune teller knows what the final result is going to be.