If you don't have bank clients in the aviation industry, you probably missed the recent OFAC Advisory, Deceptive Practices by Iran with respect to the Civil Aviation Industry. That document showed the extent to which Iran has accessed prohibited US aviation technology and equipment, through third countries. No matter what your clients' field or industry, they must be on the alert for similar Iranian tactics, involving their products and services.
For that reason, obtaining End User Certificates should never be an option,but a mandatory component of all sales to the Middle East, as well as Sub-Saharan Africa. OFAC will certainly come knocking, and your clients had better have an effective AML/CFT compliance program, as well as End User Certificates on file. It is suggested that they be signed by two senior officers of your clients' client, have the corporate seal, and be notarized, to verify that it is the act and deed of the recipient company.
Readers who wish to review the OFAC Advisory may access the complete text of the 8-page document here.