There are two types of search engine optimisation white hat and black hat optimisation. White hat optimisation techniques are those that are in line with Google Webmaster guidelines and web standards. Black Hat techniques are those that Google frowns upon, but still can work to get you the search engine results that your business needs.
Whilst Black Hat techniques might get you ranking on Google, your business will be vulnerable to a Google Slap where your website is banned from its search results or penalised for the black hat techniques you’ve used. Google is constantly monitoring and cracking down on Black Hat techniques and finding new ways to remove Black Hat websites from their listings.
For lasting results, make sure your SEO professional is using only White Hat SEO techniques so that your investment in SEO has real long-term value.
You would not want to wake up tomorrow to find out all your wonderful Google traffic is gone and never coming back. Stay away from Black Hat techniques such as keyword stuffing, redirects for non Googlebot traffic and other crazy techniques that non-professionals use.