This page describes the Auto Rental Collision coverage provided by VISA business cards:

http://usa.visa.com/business/cards/b...to_rental.html

Note this important stipulation:

This benefit is primary and provides reimbursement up to the actual cash value of the vehicle as it was originally manufactured. However, if the rental is for personal reasons, this coverage supplements, and applies excess of, any valid and collectible insurance or reimbursement benefits from any source.

In other words, if you use a VISA Business card for a personal rental it provides only supplemental coverage.