Link sales practice has been cleared stated in their webmasters' guidelines as something which could lead your sites getting penalized. However, none has been mentioned about exchanges but my assumption is that they don't carry weight like they used to anymore.
link exchanges are fine with google but they dont carry a lot of weight these days. link sales are not allowed by google and your site will get penalized if cought
Here is the official word: http://googlewebmastercentral.blogspot.com/2007/12/information-about-buying-and-selling.html Any site showing Adsense ads has to meet the Google webmaster guidelines.
that is true. either nofollow or redirect is fine but most people buy link for link juice and PR transfer so that doesn't serve any purpose if the link is nofollow or redirect