The most competitive keyword on the planet, the big blue pineapple chair. Of course I am being sarcastic. Besides, the closest place I saw that sells big blue pineapple chairs is this one, but its not really blue. I guess I can paint them, and resell them at this page. :)
What is my point?
Again, I had a client who was contacted by an 'SEO Firm'. They drew up this huge guarantee, top rankings or your money back. My client was wise enough to send me the email exchanges, between the seo firm and himself. From what started as nicely targeted keyword phrases turned into very obscure, none relevant keyword phrases. Just like me ranking for the big blue pineapple chair. Which I am sure this page will rank number one at Google in a weeks time (I guarantee it). )