A lot of optimisation techniques that are in the short term effective at boosting a site’s position in Google are against Google’s guidelines. For example, many links that may have once promoted you to the top of Google, may, in fact, today be hurting your site and its ability to rank high in Google. Keyword stuffing might be holding your page back. You must be smart, and cautious, when it comes to building links to your site in a manner that Google *hopefully* won’t have too much trouble with, in the FUTURE. Because they will punish you in the future.
Keywords are important because they are the linchpin between what people are searching for and the content you are providing to fill that need. Your goal in ranking on search engines is to drive organic traffic to your site from the search engine result pages (SERPs), and the keywords you choose to target (meaning, among other things, the ones you choose to include in your content) will determine what kind of traffic you get. If you own a golf shop, for example, you might want to rank for "new clubs" — but if you're not careful, you might end up attracting traffic that's interested in finding a new place to dance after dark.
SEM results show to a select target audience. SEO results do not. While successful SEO and SEM strategies are driven by a plan to connect with a select audience, you can only specify that target audience through SEM. Through SEM, you can (depending on the publisher) select what audiences you want to see the search results by assigning filters based on age, location, income, habits, and more. Through SEO, you cannot specifically choose who will see your search results.
QUOTE – “So it’s not that our systems will look at your site and say oh this was submitted by a user therefore the site owner has like no no control over what’s happening here but rather we look at it and say well this is your website this is what you want to have indexed you kind of stand for the content that you’re providing there so if you’re providing like low quality user-generated content for indexing then we’ll think well this website is about low quality content and spelling errors don’t necessarily mean that it’s low quality but obviously like it can go in all kinds of weird directions with user-generated content…” John Mueller, Google 2019
Ask for a technical and search audit for your site to learn what they think needs to be done, why, and what the expected outcome should be. You'll probably have to pay for this. You will probably have to give them read-only access to your site on Search Console. (At this stage, don't grant them write access.) Your prospective SEO should be able to give you realistic estimates of improvement, and an estimate of the work involved. If they guarantee you that their changes will give you first place in search results, find someone else.