Ok, I would like to know how much these people are charging you.
In a nutshell, and I am able to comment as i have substantial knowledge in this area, NO ONE can guarantee you top of first page results on google. If you want to know the honest truth, its easy enough for you to do yourself. All you need to do is make sure the phrases are all on seperate pages and the phrase is in the Web page title, The Actual header of the text and sprinkled throughout your page in the writing. Once you have this covered you need to build links back to your pages from other sites, but the link needs to be something called and anchor text, which means basically, that it will read as "YOUR PHRASE" but when you click it it will take you to the address of your page. Once you have built enough links back to your site, google will start pushing you up the rankings...hopefully.
Google is a fickle animal and the way websites are ranked is based upon a mathematical algorithm. So really its pot luck as no one on this earth knows the real requirements to make you rank high. Those are the words from Google themselves. If you want to know more information on this area search on google for a guy called matt cutts and also for Search engine optimisation for beginners.
Hope this helps.