SEO influences, but does not control the SERP results. Therefore there is no guarantee that seo process, whatever it is, can guarantee the results.
It should accurately be called a "best practice" service. An search engine optimization expert will make his best attempt to increase your presence and ranking in the search engines.
All is well, but can a good amount of ethical efforts guarantee results. It has been seen that many SEO experts have been able to trick with google via unethical practices. After all, Google is a software, not a human being. There is no information that Google has artificial intelligence in it's matrix. Means, their are chances to trick it's bots and algorithm.
Yes, it's agreed that it's not possible for a long run but, can, though for a short term, such efforts be useful?