If you're in the grey area, the trick is to get approved by the algorythm without triggering human review:
:Any sign of copyrighted material in text or on images (ad and lander): avoid logos, posters, trademarks, product photos with brand names, etc
:Any sign of gambling (sport betting included), nudity, violence, payday loans, weapons, drugs, alcohol, dietary supplements, fake documents.
:Targeting kids.
:i) Lander\prelander on domain owned by you ii) com/net/org/co.th iii) old iv) domain name is related to your campaign.
:Ad account history - if you have history of rejections, start over and run 1-3 fake campaigns to get positive record.
:Spelling, grammar, good language.
:Avoid naming your target audience directly in the ad text and lander (e.g. "for students", "young singles"), describe product instead
:Avoid sensational claims, e.g. "Success Guaranteed", "100% Result", "Best product", etc