Claim
This is the rule I'm strictest about with myself. Every metric, every "we drove" number, every aggressive round — it has to trace to a customer quote, a Wayback snapshot, a press release, a repo commit. If it doesn't, the claim is "unverified" and I either find the source or drop the claim. Composite quotes don't exist. Invented metrics don't exist. Round-numbers-that-feel-true don't exist.
Mechanism
PMM credibility compounds and decays the same way. Every fabricated claim that gets caught burns the trust that the verified ones earned. The cost of saying "unverified" is small. The cost of getting caught making one up is the whole portfolio.