Question:

What does Google say about landing pages?

Answer:

“Provide relevant and substantial content”

Link to the page on your site that provides the most useful information your ad suggests.
Distinguish sponsored links from the rest of your site content

Don’t require users to register for information.

Have pages that provide substantial and useful information to the end-user.

Provide content, not links to content

Have unique content.

Users should be able to easily find what your ad promises.

Conclusion: Google uses these points as a model for site review.

The real bottom line is: Does your site(not a product on the site) help solve the
specific problem the ad advertises?