ISP responses to DOS/DDOS attacks for customers

Is there a standard/general level of response that ISPs should provide when responding to DOS/DDOS attacks for customer networks. We try to respond and help any customer with identifying and resolving the problem since most of our customers don't have the staff to respond appropriately. How far should we go? If this issue has already been addressed, please respond off-list with the correct direction to search. Regards, Wayne