The thing to remember is that Google wont penalise you for doing this. Buying a text link won’t make you worse off than if you hadn’t bought it. That would be madness – every website that advertises anywhere would be screwed.
All Google will do is discount the value, so they have little or no effect on your ranking.
So if the reason you are buying the link is because you want a SE boost, then think twice.
If the reason you are buying the link is advertising for direct clicks, go right ahead