If you wish to accept 0 confirmation transactions, then you need to ensure RBF is disabled. If you receive an RBF enabled transaction, you should wait for a minimum of 1 confirmation.
Of course it is mandatory in every transaction if we do it without escrow.
But I've also heard that 1 confirmation is not completely safe but it will be safer if the transaction has reached 4-5 confirmations. I forgot how confirmation was declared unsafe, maybe you still remember about that? I remember about the 51% attack, can they cancel a transaction that already has 1 confirmation?