How To Keep Your Website From Dropping In The Search Engines
SEO companies often engage in one tactic that almost guarantees your website will be penalized at one point or another - link buying. Buying links has long been a popular method of increasing the number of backlinks pointing to a person's website.
When your SEO company buys backlinks to your website, however, you signal to Google that your site is in violation of its terms of service. It's especially obvious if you embed code into your website that makes it obvious what you're doing. Companies like TextLinkAds are pretty easy to figure out since they use plugins and some code that you embed into your website. If Google stops by to check out your site, you're toast.
However, manually placing links on your site can raise a red flag too. If you place links to websites that have nothing to do with your website, or if other websites that have nothing to do with your website start linking to you, it looks suspicious. Of course, Google is less likely to penalize you if irrelevant websites link to you. However, they're unlikely to have mercy if you are the one selling links on your own site and linking out to other websites.
What To Do If You're Determined To Buy And Sell Links
Maybe you think Google is a hypocrite for breaking its own TOS when it promoted Chrome through purchased links and sponsored thin content. If you're determined to buy and sell links, go into this game with your eyes wide open. Don't complain when Google catches you breaking its TOS. You'll likely get penalized. Take your lumps and move on.
Don't make it obvious. If you're going to sell links on your site, make sure the sites you link out to are at least relevant sites. If you're a website about cars, sell links to other automotive websites, or places that sell automotive parts. If you're a health blog, sell links to other health-related sites. Put the links within your content and not in the footer, header, blogroll or any other idiotic place where Google will easily catch you.
Finally, if you're going to buy links, only buy links from reputable websites that are in the same niche as you. You have to trust that the people you're buying links from won't engage in behavior that will get them nipped by Google. If the sites that link to you go down, and Google discovers the link pattern, you're dusted.