Should I be using NoFollow?

[FredAt]

I am currently in the process of exploring and understanding the issues involved with selling advertising space on my site. I am wary of falling foul of Google by selling links via ads and not marking them as NoFollow. However, I have spent some time looking at some very highly respected sites and much to my surprise I find that links that belong to ads are often not marked as nofollow. Or perhaps I am misunderstanding the code I see? I fail to see how since I am pretty sure that Google too will see the same code. I would much appreciate views and advice on this subject from those on this forum who have more experience of this subject than I (who have none whatsoever)

[maximillianos]

I think nofollow is mostly used to thwart potential comment spam.

For selling links, it is not necessary. But if you want to avoid any potential problems that go along with the negative perception of selling links, you can always just use javascript to display the links.

[bwnbwn]

"I think nofollow is mostly used to thwart potential comment spam"
maximillianos yes and no a no follow is used for a variety of reasons page rank flow through the site, links to outside the site, and of course spam contol.
here is a good quote

(Matt's precise words were: The nofollow attribute is just a mechanism that gives webmasters the ability to modify PageRank flow at link-level granularity. Plenty of other mechanisms would also work (e.g. a link through a page that is robot.txt'ed out), but nofollow on individual links is simpler for some folks to use. There's no stigma to using nofollow, even on your own internal links; for Google, nofollow'ed links are dropped out of our link graph; we don't even use such links for discovery. By the way, the nofollow meta tag does that same thing, but at a page level.)

A no follow added to the links won't tell google a thing just that you don't want to pass PR to those pages.

[FredAt]

Thank you. I have noted that some of the reputable sites do ads like this

a. The ad onclick calls a PHP script with an ad id as parameter.
b. The script redirects the browser to the ad site.

I suppose that given that Google will never "click" this ensures that there is no PR flow, no question of link selling and everything is OK.

The thing I still don't understand - why is it that certain very reputable sites (I refrain from names since I assume this would be against forum policy) - with PR of 8 & 9 - show ads with no attempt to either cloak them from SEs or to make the ad links nofollows?

And given that they do that so blatantly why is it that Google does not penalize them? What, for instance, would happen if I were to report them to G as paid link providers?

[FredAt]

And, more to the point - would having a strict and clearly explained policy of ensuring no PR flow to ad links effectively mean that I don't get any advertisers? I am operating a fairly new site but one that is growing fast, has a very focused user group, a very high proportion of repeat visitors and a great deal of content. I assume that there are advertisers out there who genuinely want to reach that audience rather than just get PR?