wheel - 12:07 am on Jul 12, 2011 (gmt 0)
Well, I've never done it, not by type of thing. But I'm reasonably sure that I've had it done to me. And I'm surprised that it worked for even one link. If one's backlinks are high enough quality, then one should be reasonably proof to these things. But nothing's 100%.
As for ethics, if a competitor has a link they paid nothing for, and I pay the site owner $500 for the spot, then I win and the site owner wins by $500 and the competitor sucks at business. That's ethics for you.
Now on the flipside, I came across a dofollow ad today. I was reasonably certain that the ad had probably expired and was simply there because the site owner never took it down. Asked the owner how much to put my link there. Well, turns out the ad wasn't expired yet (I think this may be an interesting tactic - if a link looks old, it may be worth pursuing with a current suggestion) - but they told me not only could I have the ad/link once it did expire, but that I could actually have it for free. So is that a paid link?