If your winnings are reported on a Form W-2G, federal taxes are withheld at a flat rate of 24%. If you didn't give the payer your tax ID number, the withholding rate is also 24%.
Casinos want to pay you. They are legally required to pay you, and it's in their best interest to avoid bad publicity. But they will follow the law exactly. Most of the reasons why a casino may not be able to pay you are easily remedied.
