Structured data should match what the page says
A website can contain technically valid JSON-LD while describing something a visitor cannot see. This is not only a syntax problem: structured data should represent the actual content of the page.
Start with what readers can see
Google Search Central’s guidelines call for information that is current, relevant and visible to readers. They prohibit fake reviews and content unrelated to the page’s main subject. Markup describes the page; it is not a place to add promises that the public text does not support.
For a small business, a useful check is to compare each marked-up fact with the place where it appears on the website. Does the name match? Is the date still current? Does the image represent the subject? If you cannot find the fact on the page, review why you are publishing it in the markup.
Choose the appropriate type, not the most striking one
Google recommends using the most specific applicable types and properties and following the rules for the particular feature. A type existing on schema.org does not mean every use of it has a special appearance available in Google Search.
Before implementing it, read the documentation for the feature you want to describe and identify its required properties. Recommended properties can add context when real data is available. Do not fill fields with invented information just to make a test look complete.
Passing a test is one check
The Rich Results Test and URL Inspection can catch many technical errors. Google also warns that correct markup does not ensure a rich result will appear: other criteria and quality guidelines still apply.
After changing content, review the JSON-LD too. An old opening time, date or image can remain in place after the visible text has been updated. Keep a shared data source where possible and check the published page, not only the template. The aim is consistency between what you explain and what systems can interpret.