A Casino except chargebacks to a certain degree, it is all about how strict the fraud department is. Most Casinos can probably get away with a 0 % chargeback for a period of time, but that would mean that the fraud department is to effective and is also blocking legitimate players as well.
I reckon a charge back rate is aprox around 2% for an average Casino.
If a person claims a chargeback it is very hard for the creditcard company to refuse it if it has never occured before on that creditcard.
Henrik