Other than a few selected few at the kingdom of Google and co, no one really knows for sure which link gives you more authority, which link is passing juice and which link is discounted straight away. We make assumptions, we test, we analyze, and sometimes we come very close to the actual workings of the engines. If you’ve ever analyzed the backlinks profile of a successful site over a long period of time, you’ll notice that their link building profile looks natural and natural doesn’t only mean little or no paid links but seems at time quite all over the place.
There are over 20 unique backlink factors I’d like to call natural link building indicators which shade light on this type of strategy. Needless to say, as a long term search engine optimisation strategy, natural is good, but it doesn’t mean you can’t gently nudge the strategy your way provided you keep within the guidelines.
20 Indications That Your Link Building is Natural:
1. No paid links, link farms, bad neighborhoods etc
2. Some of the backlinks to the site are image links
3. Some of the image links, dare I say… have no alt text and the image name has nothing to do with the site
4. Some text backlinks will contain your keywords… result!
5. Some of the text backlinks will contain the metadata page title
6. Some of the anchor text might include unoptimized terms such as ‘click here’, ‘find out more, ‘ here’ etc
7. Some of the backlinks are likely coming from bloggers
8. Some of the backlinks are likely coming from forums
9. There’s minimal or no use of directories as an SEO strategy
10. There’s minimal or no use of article submission as an SEO strategy
11. You’ll see a few indications of PR generating some quality backlinks
12. In terms of IP geo location, some of the backlinks will come from territories you’re not really targeting
13. TLDs likely to include some .org and .edu/.ac will only further help
14. A large percentage of pages linking out to the site will have no or low PR
15. A large percentage of the sites linking out will link from deeper pages… not just the homepage
16. Some links will include foreign language anchor text or surrounding text
17. Some of the links will lead to 404s, it happens some people won’t link correctly so make sure you fix this
18. The number of backlinks is growing constantly
19. Backlinks to the site are spread across many pages, not one or two highly optimized pages 
20. Some of the links might come from less reputable sources without your doing, but you’d assume Google knows that and would simply discount those links
You’ll be wise to try and ensure your link building looks as natural as possible, especially if you’re counting on search engine optimisation as a marketing strategy for the long run. Ensure that your content is fresh and update to date, that you have basic tools to share content (a la addthis and co) and that you understand that taking a shortcut right now might mean quick wins, but a poor long term strategy.