Download Visa and MasterCard critical bulletins click (PDF)
MasterCard Acceptance Rules updated June 2013
Chargeback Management Guidelines for Visa Merchants (2012) As of June 2013, Visa last updated 2011.
Visa International Operating Guidelines (2013) April 15, 2013. Over 1,200 pages of information including comprehensive dispute and chargeback information for merchants.
Visa PCI DSS Compliance Validation Framework November 18, 2008
Visa USA Data Security Alert POS PIN Entry Device Vulnerabilities November 19, 2007
American Express Merchant Policy Guide (link to site)
Discover Merchant site
Visa comprehensive download library (official site) includes:
E-Commerce Merchants’ Guide to Risk Management PDF | 1.7mb