SEM search results have ad extensions. SEO search results have featured snippets. When comparing SEM vs. SEO, you’ll also find differences in the appearance of the search results. SEM search results may include ad extensions, which can add on additional links, phone numbers, and callouts. On the other hand, SEO results may appear with featured snippets in search.
You can confer some of your site's reputation to another site when your site links to it. Sometimes users can take advantage of this by adding links to their own site in your comment sections or message boards. Or sometimes you might mention a site in a negative way and don't want to confer any of your reputation upon it. For example, imagine that you're writing a blog post on the topic of comment spamming and you want to call out a site that recently comment spammed your blog. You want to warn others of the site, so you include the link to it in your content; however, you certainly don't want to give the site some of your reputation from your link. This would be a good time to use nofollow.
Black hat SEO attempts to improve rankings in ways that are disapproved of by the search engines, or involve deception. One black hat technique uses hidden text, either as text colored similar to the background, in an invisible div, or positioned off screen. Another method gives a different page depending on whether the page is being requested by a human visitor or a search engine, a technique known as cloaking. Another category sometimes used is grey hat SEO. This is in between black hat and white hat approaches, where the methods employed avoid the site being penalized but do not act in producing the best content for users. Grey hat SEO is entirely focused on improving search engine rankings.
On October 17, 2002, SearchKing filed suit in the United States District Court, Western District of Oklahoma, against the search engine Google. SearchKing's claim was that Google's tactics to prevent spamdexing constituted a tortious interference with contractual relations. On May 27, 2003, the court granted Google's motion to dismiss the complaint because SearchKing "failed to state a claim upon which relief may be granted."