I intend to launch a site that displays, among other things, user supplied articles. At present I have validation on all input that rejects links.

After perusing other sites that host articles, it is obvious that many users post articles with the intention of inserting a link.

I was thinking about allowing such articles(with links) for a nominal fee.

Will this harm my site in the eyes of google etc.

I don't think that you should allow people to post free articles that don't include links or post articles with links for a fee. What's going to end up happening is your paid-for articles are just going to be spam and press releases.

Quality authors contribute content for free because it is something to add to their portfolio or to build up their name in their industry.

If you really are after good, quality content, then it's possible to get good authors to write for you for free. Give each of the authors their own profile page where they can write a small blurb about themselves or link to their own portfolio.

This way, the articles themselves won't be plugged with spam, but you're still getting the signal across that you value your contributors and want to recognize them when they contribute to you.

Thanks csgal for your input. I was particularly interested in what, if any harmful effect such an idea would have.
I'm not sure that I have a problem with an advertising type article, so long as it is written as an article. Thorough monitoring might discourage the spam aspect. After all, the advertising you have here on daniweb, is spam to everybody who does not respond to it.
Is the concept of selling links, in the way I've described, detrimental to a site from the perspective of search engines?

I think I would need a better explanation to be able to say, one way or another, whether it would be considered SE spam.

However, what I'm concerned about is that articles that continuously plug the author's website/company will just be seen as press releases.

People come and read DaniWeb for its content ... we have ads surrounding the content, but it's the content that people come to read. If the actual content are just press releases and promotions, no one is going to read it.

Yup, content is the key factor.

I see your point people and I agree that it's content that matters. I think the 'selling links' title might have been somewhat misleading.

In the normal course of events, article input is validated to ensure no links are posted. I thought that some users however would want to post links and provided that they did so in the form of an article it would be acceptable. I propose to charge a nominal fee for this.
Now obviously, if I had just one page of articles, it could indeed be seen as a list of press releases and I agree that it would have little interest for users.

The fact is, I'm relaunching my site within the next week or two and it's huge in its scope. There will be about 25,000 news sections, 25,000 article sections and 25,000 separate forums. Each of these 75,000 sections is then split into sub-categories. Any advertising type articles would be in appropriate sub-categories in appropriate sections and consequently well spread out(hopefully).
You can see that one paid-for link in each section would generate substantial income

Many news articles need to link to sources and the websites of any companies being discussed in the article. If you charge a writer because they are linking to their own website in the article, it can be considered mixing low quality press releases with high quality articles. If you charge a writer for any links in the article, I can't see you getting many authors willing to do that, because linking to resources and references is a natural (even necessary) part of a news article / editorial.

All valid points. I guess I'll have to try it and see what happens. Easy enough to change

No, you don't have to pay to put links on your website that direct your visitor to another website. It is, however, polite to send the site an e-mail through their contact and let them know what you plan on doing.