There are four options in the Google removal tool, the tool itself is automated and only a subset of requests are reviewed manually.
Google’s automated tools or manual reviewers will deny your request if it doesn’t meet the (often) technical requirements set out in their policies.
Here is a breakdown of all the common reasons why your request may get refused, there are four sections to reflect the four options in the tool:
1) The page has now been removed from the site and you see a “404 error” or the webmaster has kindly placed a piece of code on the page/site indicating that Google should remove this result. Why would Google deny such a request? find out here.
2) The webmaster has removed the offending words from the page but the page itself still exists on the web. Find out why these types of requests are denied.
3) Google has denied your request to remove a specific piece of personal info that appears in the search results. Diagnose possible issues here.
4) Solve issues related to Google’s Safesearch results and adult or inappropriate images.