Recently there has been a spate of well publicized court cases against SEO companies who have been involved in dubious practices such as making false claims or false guarantees. That is why it is essential to hire an ethical SEO company.
It has become clear that companies operating within the industry must become accountable for what they claim. In terms of search engine rankings it is impossible for an organic SEO company to guarantee specific placement. This is because organic SEOs do not control the search engine rankings. The rankings are controlled only by the individual search engines. Therefore SEO companies must set realistic claims in their communications with clients.
The truth is a guarantee by a SEO company relating to rankings means little or nothing. What the SEO company should be offering is a guarantee that they will work with the utmost dedication and diligence towards getting your site ranked.
In reality that is all that they can guarantee.