You need to make sure every single client fills out a credit card/ debit card authorization form before you provide any services for them. That's it. Full stop.
Collecting client payments is a headache to begin with. Planning ahead by making sure the proper documentation is in place can help to mitigate losses later. Client's can be upset by deductibles and limitations on insurance plans, and not want to provide prompt payment.
Collecting a valid credit/debit card from your client, alongside authorization to charge the payment method for the amount due when they complete intake paperwork is vital. Insurance benefit estimates, are just that; estimates.
Sometimes, a change in what the expected client responsibility would be can cause a payment dispute. Literally. Some clients will actually dispute the payment that you are owed, once charged. Keeping a signed credit card authorization form on hand will be a great tool should any documentation to fight any chargebacks in the future, is needed.