Check out this must-read article on Google’s recent SEO changes: http://affiliateblackbook.com/go/micromasters
In summary, Google is targeting unnatural inbound linking. Sites with overly high percentages of money keywords in their inbound links – the keywords you’re trying to rank for – are getting hit hardest.
The above article explains, with proof data, exactly what’s going on.
Two Cents from X
There is a lesson you will learn eventually, as I have – there are no shortcuts. All attempts at gaming Google will eventually bite you in the ass, rendering months, even years, of effort useless.
My advice, which you would be wise to take, is to worry less about manipulating Google for a quick gain – and to worry more about the playing field, your competitors in a niche that you’re competing with.
More specifically, are you providing a better value? Better information? Easier to digest? Unique, exclusive and valuable? If the only thing you’ve got to hang your hat on is the discovery of cheap link builders on Fiverr or the WSOF . . . think about it.
Stay away from all that crap – stay away from anything that promises to make you look better than you are, than what you’ve earned. Instead, work on delivering something more valuable to people – and if you’ve hit the nail on the head the market will do your linking work for you.