I will briefly touch on one of the most important things to look for when hiring an SEO company. Look for a company that includes a portfolio or case study section on their site. It is important to have at least a glimpse into the type of work the firm has done in the past.
Here is a perfect example of a company that is probably a complete waste of money. Besides their obviously poor English skills and the fact that they offer search engine submission as part of their service. The portfolio page, http://www.bluedelightconsultant.com/portfolio.html is just a collection of barely recognizable images with no live links and no mention of what terms they achieved ranking for.