What should bloggers avoid doing that can hurt their SEO? Can you explain what whitehat, greyhat and blackhat SEO are?
I'd personally rephrase the question as, "What are the search engines' current guidelines that bloggers should know about?" The guidelines, which shift on a continual basis and are enforced in a variety of ways, define what is "whitehat," what is "greyhat" and what is "blackhat SEO." In a nutshell, whitehat SEO means approved practices, greyhat SEO is borderline stuff (which, like paid links did, can easily shift into Google's definition of blackhat SEO) and blackhat SEO is 100% against guidelines.
I'd like to debunk the nonsense that whitehat SEO is ethical, greyhat is getting shady and blackhat SEOs are on the verge of being axe murderers. Actually, they use spears, not axes. Just kidding.
More seriously, the only point where ethics arise is in terms of what you're promoting, and whether you're vandalizing others' websites to do it. For instance, I have a friend at Slightly Shady SEO who does SEO for products you could find in a local outlet store. But some others promote products that are detrimental to buyers, by selling them extra credit lines that they don't need, for example.
And as to vandalizing websites, most spammers stuff links to their sites into vulnerable wikis, blogs and other content management sites that let you submit links. There's also outright cracking where a site gets broken into, and Viagra or other 'pharmacy' products are added to the site. Typically this happens to universities, whose powerful domain names help get spam ranking for competitive queries. My school, McGill University, recently saw one of its departments' websites hacked and ranked for 'buy Viagra' or something like that.
Concretely, there's two more points I want to share.
First, trading links indiscriminately is a bad idea because search engines won't rank you any higher for it and you risk penalization. A whole bunch of real estate sites got slammed for doing this, in an effort by Google to make examples out of them. That doesn't mean that your swimming blog can't link to your brother's anime blog. Just make it clear why you're linking and you should be fine.
Second, your site's security and defenses against crackers is increasingly important. While McGill's sites won't get banned if they're hacked, your average blog could. The difference is that McGill has a brand. If McGill doesn't show up when people look for McGill, Google looks bad. But if your blog with no brand awareness (especially as measured by search volume for your personal name/blog name) dissapears, who'll miss it?
If you want to take action right away, make sure that your version of WordPress is the latest one (currently 2.5) and that you add patches as they're released. There are some excellent references on the topic I encourage everyone to read, and particularly the case study of CornwallSEO who got cracked and had a marker alongside their site in Google's search results saying that their site was no longer secure and might expose your computer to spyware/adware/viruses and other junk:
- SEO and internet security (Hamlet's a technical pro, and I encourage you to check out his new RankSense SEO software for helping automate certain tedious SEO processes. He's also a friend - note again the power of friendships for link building!)
- Wordpress Blogs not Being Indexed
- Living Without Google
- Google Proxy Hacking
To summarize: If you're very risk averse, just blog and don't sell links. If you think you can buy/sell links without getting noticed, and aren't overly worried about penalties, you can try that too (besides my post on disguising paid links above, I recommend Brian Chappell's 30 Tips for Buying Links and Rand Fishkin's Buying Links Under the Radar. And if you're highly aggressive... well, the question was about avoiding running into trouble with one's SEO, so this is kind of going beyond the scope of it.
Oh, and on the same note of ethics - Google's no beacon of shining hope itself, so take its admonitions with a grain of salt. Consider this quote from leading SEO expert Aaron Wall, "Google paying AdSense scrapers to steal your content makes Google a pretty dirty company."
