According to Google Webmaster Guidelines, the answer is “YES”.
If you are paid or compensated in any way for those links, then yes, you have to use “no-follow”. This allows the searches to be more accurate, because they wont incorporate any paid links into their calculations. From the horse’s mouth:
Buying or selling links that pass PageRank is in violation of Google’s Webmaster Guidelines….
Not all paid links violate our guidelines. Buying and selling links is a normal part of the economy of the web when done for advertising purposes, and not for manipulation of search results. Links purchased for advertising should be designated as such. This can be done in several ways, such as:
- Adding a rel=”nofollow” attribute to the <a> tag
- Redirecting the links to an intermediate page that is blocked from search engines with a robots.txt file
What this means is that buying and selling links is normal for advertising purposes. But if a link is purchased, it must be designated as so with a no-follow tag.
1. Add your copy to your Post or Page edit screen. Select it, and click on the link icon.
2. Complete the link screen with your link, and title.
3. Change to HTML view. Place your curser just before the end of the “A” anchor html tag.
4. Add the new attribute [ rel=”nofollow” ] without the brackets.