Is there any customization in OBAS which would allow processing of billing documents without respect to customers account balance and credit limit value? As a result order would be always processed, subscriptions never gets expired, etc.
No, there is no such customization implemented. Account balance is one of the key concepts of any billing, it can not be neglected.
Please take a look at the
Credit limit option. As it is stated in OBAS Provider's Guide:
Credit limit value - the maximal amount an account can owe a vendor. While a credit limit is not overdrawn, a customer orders are completed automatically, before payment is applied. When a credit limit is overdrawn, ordered services are provided only after a corresponding order is paid. A special event is provided in OBAS when credit limit becomes overdrawn - event ID 23 'Account credit limit has been overdrawn'. Both customer and vendor receive notifications when such an event happens. The actions over subscription (put on hold, etc.) can be set specially in the Event Manager. Credit limit can be also set per customer account and in this case the credit limit set in credit terms will be overdrawn by the value set in account properties.