By hiring a full service SEO firm, the users trust that they'll follow the "Best practice" guideless which have been set by Google. However, in doing so, it's important to understand that progress may not be immediate. Sometimes the strategies do work instantaneously. However, there is no guarantee that this will occur. In fact, no results are guaranteed. A good SEO firm will not make promises. Rather, they'll be able to show them by example that they can improve an organic search presence and the expectation will be that they'll get these results, too. Beware of any firm that makes promises and sets guarantees.