How do you define endorsement? What situations involving endorsements have you encountered that either don’t appear to be addressed by the guideline or aren't clear?

Ethics Tenet 12 - Guideline: Endorsements, says:

Members should not endorse commercial products or services by agreeing to use their photograph, endorsement, or quotation in paid or other commercial advertisements, whether or not for compensation. Members may, however, agree to endorse the following, provided they do not receive any compensation: (1) books or other publications; (2) professional development or educational services provided by nonprofit membership organizations or recognized educational institutions; (3) products and/or services in which the local government has a direct economic interest.

Members' observations, opinions, and analyses of commercial products used or tested by their local governments are appropriate and useful to the profession when included as part of professional articles and reports.

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Tenet 12 of the ICMA Code of Ethics