Just like with natural or organic search engine rankings, it’s not possible to guarantee top placement in Google adwords paid search. AdWordsPro a member from Google groups says that a company guaranteeing a specific position in paid or unpaid search engine results is potentially unethical and not feasible
Bottom line, if anyone says they can ‘guarantee’ top placement – whether in the unpaid search results or within AdWords – then buyer beware.
Google’s AdWords algorithm is not based on how much you are willing to pay for placement. Paid search ranking factors include click through rate, the quality of your pages, Quality Score, landing page relevance, overall website relevance, ad title & copy, keyword relevance, usage of Dynamic Keyword Insertion.
Barry has more on the paid search guarantee.