QUOTE: “If you have comments on your site, and you just let them run wild, you don’t moderate them, they’re filled with spammers or with people who are kind of just abusing each other for no good reason, then that’s something that might kind of pull down the overall quality of your website where users when they go to those pages might say, well, there’s some good content on top here, but this whole bottom part of the page, this is really trash. I don’t want to be involved with the website that actively encourages this kind of behavior or that actively promotes this kind of content. And that’s something where we might see that on a site level, as well.” John Mueller, Google 2016
QUOTE: “high quality content is something I’d focus on. I see lots and lots of SEO blogs talking about user experience, which I think is a great thing to focus on as well. Because that essentially kind of focuses on what we are trying to look at as well. We want to rank content that is useful for (Google users) and if your content is really useful for them, then we want to rank it.” John Mueller, Google 2015
QUOTE: “Some Low-quality pages have adequate MC (main content on the page) present, but it is difficult to use the MC due to disruptive, highly distracting, or misleading Ads/SC. Misleading titles can result in a very poor user experience when users click a link only to find that the page does not match their expectations.” Google Search Quality Evaluator Guidelines 2015
The SEO starter guide describes much of what your SEO will do for you. Although you don't need to know this guide well yourself if you're hiring a professional to do the work for you, it is useful to be familiar with these techniques, so that you can be aware if an SEO wants to use a technique that is not recommended or, worse, strongly discouraged.