Whitey - 9:15 pm on Feb 21, 2010 (gmt 0)
Link sellers certainly run a risk , yet i've see nsites that have been around for years with no problems.
Link buyers - raising your TBPR to silly heights from unrelated sites , over buying or creating a noticeable pattern with paid inbound links etc etc ....
.... it's all running a risk of editorial review , competitor scrutiny , algorthimn changes [ future or current ].
So the moral of the story is , the more you test that threshold , the higher the risk of a problem.