There is no doubt that the Gray-hat Search Engine Optimization strategies are a good SEO strategy but you need to take proper care while using such techniques. Gray-hat Search Engine strategies are on the boundary of being banned as SEO practices.
My sincere advice to you would be to make yourself aware of most common issues that you can face while using Gray-hat SEO strategies. No one can disagree with the fact that this set of techniques will boost your website's performance but a slightest of slip or miscalculation can lead to adverse effects.
Cloaking
This SEO strategy is a part of the Black-hat SEO techniques. In this technique various redirects are used with sources originating from an already structured page that may display different information to the Search engines than what is really seen by the person visiting the web page. However there is a disadvantage to this technique. The disadvantage is the poor effect it causes to the user visiting the website. This technique can only be used for a short time period and you need to do enormous reviews to get your website off the hook when spotted.
Although the SEO technique of Cloaking is valid but when used without proper knowledge and permission presents an opportunity for your competitors to report your website as the one that is using fraudulent activities. This can lead to serious consequences.
Link Purchasing
In this SEO technique, you may need to shed in few extra expenses. In it you would get good search engine ranking but with the high cost involved it is usually avoided my most of the SEO. The search engines would normally allow you to purchase links if it is only confined to advertisement. It goes like this, "Greater the page rank of the linking page, higher would be the cost associated with it".
This technique is solely based on the fact that you can increase the relevancy of a website by increasing the quality of links associated to it. This technique may push aside your rest of the marketing efforts as all the energies and resources are focused on achieve a high ranking by the use of the link purchasing technique.
Many SEO use this technique to bring up the overall website ranking, but it is not a good technique. One should never compromise on the content and just try misleading search engine results. This approach lasts only for short time and can also affect your website's popularity in the long run.
Micro-sites
This is another SEO technique which most of the SEOs do to promote their website and increase the search engine rankings. The SEO done through Micro-sites often avoid detection particularly when micro-sites are established using Class-C IPs. If at all you get successful in dodging the search engine, there are few chances that you can do the same with your competitors. This technique acts as a success because various search engines fail to index ownership of the web pages.