Do not do this to your links.
(1) Placing a form on your site and then allowing anyone to add a link to your site using an automated process. If you do not manually approve these links, well, you are asking for ?link problems?. Manually approve these links before posting them. What works, takes work?

(2) Denying a link based solely on a low or non existing PageRank. What a mistake! PageRank is not only outdated, it is also less relevant that it was in the past. As long as it is related to your site, what really matters here, is that the site your are reviewing is indexed or not. That is the key issue, not its popularity. This also applies outside the regular sites circle, to niche directories, smaller engines, etc.

(3) Sites that exchange links with you, but at a later time they do a ?nofollow? on your link, or they just simply take it down. That is why you need to check your backlinks periodically to verify the status of these links exchanges.

(4) Sites with faked PageRank. Yes, they are all over. The problem is that you are doing an exchange link or buying a link from a site that doesn't have the PageRank they claim to (offending domains use a 301 or 302 redirects that point their sites to sites with a high PageRank) and instead getting your genuine PageRank added to them as a trade, or your money.

Considering link exchanges.
This one is not easy, (see above) but also a good way if done right. How? Well, to start look for sites with lots of quality content that is directly related to yours. In this area, articles that are good introductions to your products or services create an opportunity. Focused on your visitors, look for resource pages that would increase their experience. Look for forums that allow actual links to be passed, as there are lots of then available, especially from authority sites, educational and governmental entities. And last, but not least, look for ?information paths?, in other words, pages that lead visitors to additional information on a product or service.

Article swapping for links.
This one is very good. When you swap articles with a related site in your industry (for the most benefit) plus you add your own comments (preferably in a different color, hint: blue) to the article you are posting on you site (to avoid duplicate content among other things) this allows you to have additional content on your site, plus the immediate benefit of a properly implemented reciprocal link.

By Utah SEO Jose Nunez