You can inactivate a customer from your Patron Database, but there is no way to permanently delete a customer.  Patron records are tied to orders, so we cannot delete a customer that has any orders associated with the record -- paid, declined, or otherwise.

When you view a customer from your Patron Database, you have the option to mark the customer as "Inactive".  When you do searches in your CRM for a subset of patrons, we exclude inactive customers by default.