It depends what your selling and how quickly you need customers. For some using Google adwords and other such ad services provides clicks and traffic right away. Eventually most if not all sites need SEO, the key is finding someone that can actually do what they promise and not waste your time. If need a couple recommedations I can help you, one of the best I've found is High Rank Websites. I only work with attorneys but I know they do a great job. Hope this helps.