QUOTE: “Keyword Stuffed” Main Content Pages may be created to lure search engines and users by repeating keywords over and over again, sometimes in unnatural and unhelpful ways. Such pages are created using words likely to be contained in queries issued by users. Keyword stuffing can range from mildly annoying to users, to complete gibberish. Pages created with the intent of luring search engines and users, rather than providing meaningful MC to help users, should be rated Lowest.” Google Search Quality Evaluator Guidelines 2017
Does this article have an excessive amount of ads that distract from or interfere with the main content? (OPTIMISE FOR SATISFACTION FIRST – CONVERSION SECOND – do not let the conversion get in the way of satisfying the INTENT of the page. For example – if you rank with INFORMATIONAL CONTENT with a purpose to SERVE those visitors – the visitor should land on your destination page and not be deviated from the PURPOSE of the page – and that was informational, in this example – to educate. SO – educate first – beg for social shares on those articles – and leave the conversion on Merit and slightly more subtle influences rather than massive banners or whatever that annoy users). We KNOW ads (OR DISTRACTING CALL TO ACTIONS) convert well at the top of articles – but Google says it is sometimes a bad user experience. You run the risk of Google screwing with your rankings as you optimise for conversion so be careful and keep everything simple and obvious.
Google has a LONG list of technical requirements it advises you meet, on top of all the things it tells you NOT to do to optimise your website. Meeting Google’s technical guidelines is no magic bullet to success – but failing to meet them can impact your rankings in the long run – and the odd technical issue can actually severely impact your entire site if rolled out across multiple pages.
Sometimes, Google turns up the dial on demands on ‘quality’, and if your site falls short, a website traffic crunch is assured. Some sites invite problems ignoring Google’s ‘rules’ and some sites inadvertently introduce technical problems to their site after the date of a major algorithm update and are then impacted negatively by later refreshes of the algorithm.
However, that’s totally impractical for established sites with hundreds of pages, so you’ll need a tool to do it for you. For example, with SEMRush, you can type your domain into the search box, wait for the report to run, and see the top organic keywords you are ranking for. Or, use their keyword position tracking tool to track the exact keywords you’re trying to rank for.
QUOTE: “I think there is probably a misunderstanding that there’s this one site-wide number that Google keeps for all websites and that’s not the case.  We look at lots of different factors and there’s not just this one site-wide quality score that we look at. So we try to look at a variety of different signals that come together, some of them are per page, some of them are more per site, but it’s not the case where there’s one number and it comes from these five pages on your website.” John Mueller, Google 2016

The biggest advantage any one provider has over another is experience and resource. The knowledge of what doesn’t work and what will hurt your site is often more valuable than knowing what will give you a short-lived boost. Getting to the top of Google is a relatively simple process. One that is constantly in change. Professional SEO is more a collection of skills, methods and techniques. It is more a way of doing things, than a one-size-fits-all magic trick.

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.