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It could be true. But if the casino wants to make more and spend more, the casino needs to calculate its budget before starting the promotion so that it is ready to compete with other casinos.
With many casinos operating, it will provide an opportunity for each casino to provide good service to its customers. If the customers are satisfied, they can get higher trust from the customers, increasing their rating among other casinos.
It has to be carefully planned, advertising plays a vital role in the success of a casino but it also requires a decent budget in order to gain the attention of the gamblers. Cheap advertising would usually have a poor result, so an advertiser, needs to gamble... it's not new to them because they are in the gambling business, so everything they do is just gamble, but with probability in their favor.