This tip is probably one of the simplest ways to gain links through conservation. A lot of SEO advice talks about double-checking links that point to 404 pages, as these are lost potential. If a link points to a page that doesn't resolve, it's generally accepted wisdom that the engines won't give any benefit to the domain or any particular page. Certainly, with something around 7% of all pages on the web being 404 pages (and the only way to reach them is through links), there's a lot of opportunity here.

But... There's also opportunity on the domain level. Take a look at queries like linkdomain:wikpedia.org -site:wikpedia.org - there's 600+ lost links. How about links that point to seooutdoorsrank.com (which, thankfully, we own and redirect) - 50+ links. Or those pointing to yutube.com (300+)?

Simply by purchasing common misspellings, mistypings and alternative TLD extensions, you can earn links the easy way - by conserving them. Just grab these domains and 301 redirect them to the right site. If you're seeing a number of links point to internal pages, you'd probably want to create a 301 rule (so that misspelleddomain.com/* redirects to yourdomain.com/*). It's not a huge amount of links, but I'd venture to say that depending on the size of your domain (& how hard it is to spell) and link profile, it could be anything from 0.05% - 0.1% of your links. There's probably no cheaper or easier way to add some high quality links to your site.

Now for the gray & black hat angles (which you asked us to disclose, but which we don't recommend). Taking this advice one extra tip further, you can easily see how & why domainers prize and might gain SEO value from owning misspellings/mistyped URLs and how these could potentially be leveraged against you or your competitors. Technically, it's legal to buy common misspellings of existing brands/domains, but it's not a practice we endorse. I should also mention that although I consider this gray hat, I don't see it specified in any of the webmaster guidelines, though certainly it violates their spirit.

BTW - My personal opinion is that when it comes to search engines, you'd probably need to own the domain ahead of time to get any SEO value from those links (or from 301 re-directing it). Buying a domain that's never been registered before or from a domain broker simply to get its erroneous, unintentional backlink profile is likely to have virtually no value. The engines appear to do a good job of "re-setting" a site's link profile to near-0 when domain ownership changes hands.