A testimonial needs proof of both the person and the promise
A testimonial should stay unpublished when the team cannot show that the customer is genuine and that the quote is accurate. Keep documentary evidence that the testimonial or endorsement came from the named person or organisation, along with contact details that allow the source to be verified.
Check the wording for more than a warm opinion. A line such as "easy to work with" is brand storytelling. A line such as "cut implementation time in half" makes an objectively testable performance claim, so the campaign needs a reasonable basis for that result before launch. Preserve the original quote, confirm who said it and identify any claim that could be read as a promise. Claims need to be watertight and backed by evidence, especially where trust, health, safety or business outcomes are at stake.
Sources: A matter of facts: The EU referendum and the power of mistruths, Faking bad: why marketers need to maintain standards in a post-truth world