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.
Let’s look at an example. At Yoast, we call our courses platform the “Yoast Academy.” So at first, it might seem logical for us to optimize for the keyword “Yoast Academy.” However, when we analyze traffic data, it turns out that our audience searches for “Yoast courses” way more often. So it makes much more sense to optimize for that term instead. Every company has its internal vocabulary, which often doesn’t match the vocabulary of its audience. Therefore, you should always select your keywords from your audience’s perspective. You can use Google Trends to research how often certain search terms are used compared to other terms.
QUOTE: “The quality of the MC is one of the most important criteria in Page Quality rating, and informs the E-A-T of the page. For all types of webpages, creating high quality MC takes a significant amount of at least one of the following: time, effort, expertise, and talent/skill. For news articles and information pages, high quality MC must be factually accurate for the topic and must be supported by expert consensus where such consensus exists.” Google Search Quality Evaluator Guidelines, 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.