I think it really depends on what business you are in or focused on. If all your revenues come from paid links, and linking is your business, then how can paid links be unethical? They are certainly not unethical for Google. (See Rentalo, VRBO and others.)

On the other hand, if your website is an adjunct to your business, and you get your income from the services it advertises, and by some incredible luck, longevity (or hard work!) you've managed to gain a good pagerank on Google, you'll be inundated with emails daily asking you to exchange links with sites that are manipulating the Google pagerank results (or attempting to). I dump these requests into the recycle bin immediately, especially if they are asking for a link to several third-party sites, or even MENTION the word 'pagerank' in their request.

I provide a 'freelinks' area for people to submit links to, that allows me to review the site
and decide if it meets my qualifications for linking, and if it does, I approve it - if it doesn't, I delete it. (Basically, no gambling, phishing or adult content sites.) Just about anything else is fair game for my freelinks pages. I don't consider the freelinks pages to be 'quality' links, since they are held in a data file and displayed on the 'fly'. No return link is requested or necessary.

IF I am approached by a real siteowner for a site that has real, valuable content that I think my clients would like to visit, then I go to the trouble of adding the link to my ACTUAL links page (hard-coded), and I request a return link from the submitting site.

I've followed this policy for many years, and the result has been a good pagerank for my own site. I have no plans to charge for these links, though I probably COULD at this point... It just seems greedy to me. I've gained my pagerank status through years of ethical conduct regarding links. Why mess with a good thing?

Puamana