Recently, I started using schema.org snippets. The first one was the Person snippet. I did everything according to Google recommendation except for the fact that I don't need for example affiliation field and many others. I used just description, image, name. So the next step is to test how my page will be showed in Google search result, Google Snippet Tools helps us in it. The example preview has a picture, looks great, but below the example it's written Note that there is no guarantee that a Rich Snippet will be shown for this page on actual search results and actually in google search results there is no any picture. FAQ wasn't very descriptive, I suspect there few required fields for every snippet, but I didn't find what they are.
Do you know what are required field for Person snippet (I also interested in Product)?