brinked - 3:29 am on May 4, 2011 (gmt 0)
Its much easier than you think really. When you buy a link they usually come in what forms?
sitewide, homepage, blogpost (usually with exactly 3 links) and usually have a 2 or 3 word anchor.
I would these make up of 90%+ of the paid links being sold. Not to mention a lot of sites are made only to sell links from after they gain some PR