Well, I've done a post about the top positive factors of Google's SEO, and a post about the top most controversial factors, so now I think it is time I give you the top 5 negative factors of google's SEO.
Server Is Often Inaccessible To Bots - The server is often unable to be accessed by bots and some pages may not be accessed.
Content Is Very Similar or Duplicate of Existing Content in the index - This can affect a sites hits or page rank if it is dropped because it is viewed as a duplicate.
External Links to Low Quality/Spam Sites - Some links lead to a site of poor quality or a site that is mainly spam.
Participation in Link Schemes or Activley Selling Links - Participating in the selling of links to other sites.
Duplicate Title/Meta Tags on Many Pages - Having the same tags on many pages could make locating specific pages difficult.
Manual Authority/Wait Given to Site by Google - Sometimes Google is accussed of of applying manual manipulation to a domain or page.
Rate of New Pages Added to Site - The amount and frequency of new, spiderable documents added to the domain over time.
Overuse of Targeted Keywords(stuffing/spamming) - The overuse of a targeted keyword, which results in the spamming of a site.
Very Slow Server Response Times - Sometimes the server is slow in respone or even unresponsive.
Low Levels of Visitors to the Site(Measured via toolbar, clicks in SERPs) - This could be detrimental to your site and cause it to have very little visitors.
There you have it, the top 10 negative factors of Google's SEO, hope it was useful.