That's the first thing that they'll do before they release the money to the gambler and that will come into a long investigation if they suspect that the user won that by surprise. They're always suspecting their winners if that's big money to be withdrawn.
The battle will be long into the courts if the winner don't have a lot of money to pay for all of the cost of those trials and the casino might have just to settle it for a lower amount but it's up to the petitioner/gambler if he'll agree on that deal.
But one thing we have to know is that every gambler is to win big so casino companies, management and customer care service agents should also know that so that when a gambler wins big, it should be a surprise to them, Because that the normal norm for all gamblers. Now the question says,
They're aware of that. What you're missing is them validating the win and the gambler who had won such jackpots. It's part of their business that they're anticipating someone's going to win big but they're mostly expecting that many are going to lose.
And if someone wins big, it's no longer a surprise to them and it's just like dealing with day to day life with what they do as they work inside the casino.