SEOsoon - 8:03 am on Mar 15, 2011 (gmt 0)
Interesting point Mike2010,
but why should you click on the link an you are paying for?
As far as I know, at least the most professional market places for text links are working with crawlers that verifiy if your backlink is assembled accurately.
Concerning penalties of these companies ...
I remember that Google himself hosted some SEO events TOGETHER with companies like TLA. I think aquiring backlinks is part of the link building game and Google knows it and they put up with it, also because there is nothing they can do about it.