[anona]

The 1-4% you mention is the interchange rate. This is collected by the issuing bank, and not Visa. Visa typically receives a separate flat fee per transaction. Although often payment processors will charge the merchant a flat percentage fee which includes the interchange fees, acquiring bank fees, association fees, and the payment processors fees.

Visa Europe (a separate company from Visa USA) would likely have to assume liability for chargebacks in the event that the acquiring bank went out of business without transferring it's Visa business to another bank. I'm not sure if such a situation has ever happened though. In general the liability goes: Merchant -> Payment Processor -> Acquiring Bank -> Visa.