However there are Casinos that accept zero-confirmation deposits.
Since they are custodial, their primary protection against those who'll "cancel" their transaction is to prevent withdrawals of the funds/winnings until the deposit has enough confirmations.
Rest are the rules and requirements like non-RBF transactions to qualify to that feature, I don't know if they are disqualifying txns with unconfirmed parent(s).
Usually those accepting 0-confirmation transactions do a risk assessment for every transaction. This way they can reduce the risk of being scammed to a minimum. Some of the things to assess are:
- account age
- total successful amount deposited so far
- amount being deposited
- RBF status
- fee rate compared to other transactions in mempool
- state of UTXOs being spent (confirmed or not)
- having a good number of connections to as many nodes as possible and watching their mempool for competing transactions (ie. double spend attack)