Before writing about guarantees in SEO, need to give you an idea of what it is.
SEO - optimization process of the website, aiming to create maximum site compliance to search engines requirements and user expectations.
The requirements of search engines as user expectations change dynamically. Especially search engine algorithms.
The most difficult for SEO optimizators is that search engines have become self-learning. That leads to different results in different terms. Terms can be geography, time, particular device or specific account. All this leads to the fact that search becomes unpredictable.
That's why giving any guarantee for the 1st place in search is impossible. But there are methods which allow us to identify search engines patterns at the time of analysis. The implementation of these patterns allows to get higher positions in ranking with high probability.
In the simplest consideration SEO is achieving following basic indicators of site quality.
High position or growth in ranking is mostly explained by according to these indicators.
So we can guarantee such methods implementation to your website.
Specific warranties and possible results only after studying the site and the client's business.