Google publishes three sets of rules. Breaking the content rules is what triggers manual actions.
Technical
- The page carrying the markup must be crawlable and not blocked.
- Use one of the supported formats.
- Include all required properties for the type, or the item is ineligible.
- Do not block the page from indexing.
Quality
- Content must be visible to users, not hidden markup.
- Markup must be current and accurate, a price in markup that differs from the price on the page is a violation.
- Use the most specific applicable type.
Content
No misleading, illegal, violent or sexually explicit content in markup. No reviews you wrote about yourself presented as customer reviews. No markup for content that is not on the page.
Alien Road recommends: generate structured data from the same data source the page renders from, never as a separate hand-written block. Hand-maintained JSON-LD drifts out of sync within months, the price changes, the markup does not, and you now have a policy violation nobody notices.