Google wants organic. Businesses don't have time to wait for that. So, SEO firms are hired to expedite the "organic" growth of a website. Well, then, that's not organic anymore right? Well, sort of. Few businesses make it without some form of marketing effort especially when starting up. Google wants to encourage honest hyperlinking. Not every hyperlink is honest. What used to be considered "white-hat" SEO is quickly becoming "black-hat" SEO. Here's how to know the difference.
1. Forum backlinks
Black-hat: Software generated, automatically created forum backlinks are a sure way to get a Google penalty. There have been many tools and services that automatically created forum accounts with keyword rich links that pointed to the websites of the user. These links do not work anymore and may get you blacklisted for the very keywords you're trying to promote.
White-hat: If a high quality forum is closely related to the topic of your website, a link from that forum can still have a positive influence on the search engine positions of your web pages.
2. Directories
Black-hat: Bulk submitting your website to directories that will accept any kind of website won't do your rankings much good.
White-hat: If your website is listed in a high quality directory that delivers targeted visitors to your website, you should submit your site to that directory. Links from authorative directories (including niche directories) with strict submission guidelines are good for your website. Local directories of high caliber still count! BBB, YP, Yelp, Angies List etc.
3. Guest blogging or Article Marketing
Black-hat: Using the same article or versions of the same article (spinning) on several blogs or article publishing sites doesn't work. Using keyword rich links in that article might and probably will trigger a Google penalty. If the main purpose of guest blogging is getting links, don't do it.
White-hat: Guest blogging can drive targeted visitors to your website if you write content related to your business. Your guest blog or article should offer the readers insights or other valuable information. Individual articles on related blogs can have a positive influence on your website's performance.
4. Link pages
Black-hat: If your link pages contain links to every non-relevant sites, chances are that these link pages won't be good for your site.
White-hat: highly themed link pages that contain links to closely related high quality websites are good for website visitors and search engines.
SUMMARY
At the end of the day, links that drive DIRECT traffic are better than links for links sake. Content that drives traffic directly to your site is good. Content placement that is used for the sole benefit of getting your site ranked in Google may have the opposite effect. Google is getting that good.