Bad SEO techniques will almost certainly end in failure. By attempting to game the system one of two things will usually happen. Either you will be penalised by search engines and ranked down or you will find short term success that will be undone with subsequent algorithm updates. These techniques are commonly referred to as Black hat SEO, with the exception of duplicate content and content light pages as these are often genuine oversights.
Although less common these days, agencies still implement these techniques in the hope of gaining short term, unsustainable success. They are reckless, risky, and can seriously damage a company. The list below should only be used as a reference.
Trying to cram in too many keyword phrases can work against you. Not only is the passage of text less likely to read well, search engines are also more likely to penalise you. Striking a balance is the key here. A keyword density of between 1-3% is the generally accepted way of doing things.
Using invisible text to cram keywords into a web page is a practice that was once heavily used. Before search engines put policies in place to ban this technique, the internet was rife with websites using it.
Example: You’ve created a web page that has a background colour of #FFFFFF, aka white. You would then place text on the page with an ever so slightly darker shade of white, like #FFFFF0, aka off-white. This makes the text virtually invisible to a human reader but search engine crawlers would read it as normal.
Pages with too Little Content
Content-light pages with short page view times can sometimes result in search engines downgrading your keyword rankings. Better to merge these pages together logically or add to them. Aim for a minimum of 250 words per page.
In a nutshell – The content presented to a search engine spider is different from that presented to a user’s browser. The most common way of doing this is basing the content presented on the IP address of the spider or user accessing the website.
Cloaking is often used to try and trick a search engine into giving the specific website a higher ranking. Other uses are ranking a website for a different search term than the page content shows.
Having content that is the same, or very similar, on multiple pages can incur a penalty to search results. If your duplicate content is on an external blog, for instance Tumblr, its important to link the original source (the one you want to have the ranking juice for) at the top or bottom of each post. This prevents penalties from duplicate content.
Slow and steady wins the race. Attempting to buy backlinks from people openly selling them may offer some short term success but the method itself is irrelevant and unsustainable. Better to acquire quality backlinks over time. These will likely be more useful in the long run, more relevant to your business, and won’t incur any penalties.