You have come to a conclusion that you want to hire a search engine optimization company to attract more traffic to your website. This is a piece of advice for you.
Search engine optimization consists a bunch of tactics and techniques, so make sure the SEO agency’s staff has different knowledge and skills, like web design, experience in marketing, editorial resources,  possessing business degrees is also a great advantage. Performing SEO, everything matters.

Don’t get too impressed about dealing with “SEO guru” of year 2005. We are now in 2009 and in such competitive market as Internet, they are not necessarily experts any more. Though, the info of how long the company has been is business is significant if we are talking about a period of several years.
Ask your SEO consultant what exactly will be done to your website. Pay attention if the company you contacted will be performing your competitors research. Will they drive quality traffic and conversions rather than just traffic no matter where it comes from. A professional SEO company usually have their own strategy of how to create a quality traffic.

Shady manipulations can still work, but only in the short term. This is not a good strategy you can implement, correct? Finding legitimate SEO company will save you time and money in a long-term perspective! Is it going to be a long-term relationship? Long-term satisfied clients is is what the agency you should be looking for wants to achieve.
An SEO is a hard work, it usually takes up to several months to see the results of it. This is the reason why it is so important to make a right choice from the beginning, because after you will need to give it a time, and only then evaluate the work and make your judgement.

Many “Choose your SEO company” guides are suggesting you to ask for case studies, recommendations, testimonials etc. Do you really think every successful client is willing to share with you? Of course, a professional seo agency will always have something to show you.  Actually, what is really important for you is an SEO agency itself. There is nothing more pathetic than an SEO company which doesn’t even implement the basic rules of seo.
We are not talking here about #1 ranking positions on Google,  Even Google’s own published guidelines states: “No one can guarantee a #1 ranking on Google”. Beware of these companies, a company making such promises is not trustworthy.
The last suggestion is - be realistic. Chat with seo professionals before making any decisions, do some research, what could be the amount of traffic you can possible reach, consider a redesign if your website is too old or not SEO friendly. This way you will know what to expect from an seo agency and avoid future problems and misconceptions.