So, you might never have thought about search engine optimization, and suddenly you saw this nice ad, that said "get your page high ranked in google and yahoo". You are interested? You wanna use their service?
First, I do not recommend you do!!! Check those many free tutorials and do it yourself. Because: It saves you money, and more important, you know what happens.
But, having mentioned this, and you are still interested, there is a very simple hint, to find out, whether they can really help you, or just have a nice ad:
Search for "search engine optimization"! If they rank high, they know what they are doing. If not, they only have a nice ad.
(If you are a smart guy, you wanna do the same with this article now. I have to admit, my ranking won't be high. Why? This site is not about SEO in general. It is my personal website. Serach for my name and it is ranked on top (google) or at least high.)