Any company that claims they can guarantee results is sketchy at best, and probably falls into the "run and hide from them" category.  Keep in mind that no company...NO COMPANY...can guarantee SEO rankings.  No one controls Google, Yahoo or MSN (the three major search engines).  

The rankings that appear in the search engines are determined by their proprietary algorithms, the SEO efforts of your competitors and the SEO effectiveness of your website.  For a company to claim that they can guarantee your rankings is simply them making a promise they can't hold to.  And as a business owner, I'd have to seriously wonder about a company making promises which it can't deliver on.

 

You need to make sure that they are using SEO tactics that will NOT get you banned from the search engines.  It is possible to pop up #1 overnight, however, if it is done improperly - YOU WILL NOT BE #1 FOR OVER A YEAR!