OBSERVATION – You can have the content and the links – but if your site falls short on even a single user satisfaction signal (even if it is picked up by the algorithm, and not a human reviewer) then your rankings for particular terms could collapse – OR – rankings can be held back – IF Google thinks your organisation, with its resources, or ‘reputation, should be delivering a better user experience to users.
Big sites can rank for the most general terms. Smaller sites within a very specific niche can do the same. Of course, it’s also easier if you’re writing in a language that is not spoken all over the world. For most smaller sites that are writing in English, however, the general rule of thumb is this: start with a big set of long tail keywords which have little traffic, but you can rank for more easily. Then, work yourself up to the rankings step-by-step. Once you’ve gained some SEO authority, start optimizing for more general keywords. And in the end, maybe you will even be able to rank for your head keywords!
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.
QUOTE: “While, as a whole, web usability has improved over these past several years, history repeats and designers make the same mistakes over and over again. Designers and marketers continuously need to walk a line between providing a good user experience and increasing advertising revenue. There is no “correct” answer or golden format for designers to use in order to flawlessly reach audiences; there will inevitably always be resistance to change and a desire for convention and predictability. That said, if, over the course of over ten years, users are still lamenting about the same problems, it’s time we start to take them seriously.”  Therese Fessenden, Nielsen Norman Group 2017
One common scam is the creation of "shadow" domains that funnel users to a site by using deceptive redirects. These shadow domains often will be owned by the SEO who claims to be working on a client's behalf. However, if the relationship sours, the SEO may point the domain to a different site, or even to a competitor's domain. If that happens, the client has paid to develop a competing site owned entirely by the SEO.