Before making your mind to go for a certain SEO Company, it's better if you can discuss the matter regarding all your requirements in details. Ask for their plan and the deadline by which they can work on your projects. Moreover, keep an eye for SEO companies who are interested in long term contracts. Don't get foxed by the words of SEO companies who ensure you positive results in the long run. Rather, a true and efficient SEO company will not usually lock your results for long period and even if so, there is nothing to worry about in case of genuine SEO companies. After all, you need to remember that there is nothing called instant success in SEO services. It really takes time in getting its results.