QUOTE: “What makes a page spammy?: “Hidden text or links – may be exposed by selecting all page text and scrolling to the bottom (all text is highlighted), disabling CSS/Javascript, or viewing source code. Sneaky redirects – redirecting through several URLs, rotating destination domains cloaking with JavaScript redirects and 100% frame. Keyword stuffing – no percentage or keyword density given; this is up to the rater. PPC ads that only serve to make money, not help users. Copied/scraped content and PPC ads. Feeds with PPC ads. Doorway pages – multiple landing pages that all direct user to the same destination. Templates and other computer-generated pages mass-produced, marked by copied content and/or slight keyword variations. Copied message boards with no other page content. Fake search pages with PPC ads. Fake blogs with PPC ads, identified by copied/scraped or nonsensical spun content. Thin affiliate sites that only exist to make money, identified by checkout on a different domain, image properties showing origination at another URL, lack of original content, different WhoIs registrants of the two domains in question. Pure PPC pages with little to no content. Parked domains” Miranda Miller, SEW, 2011

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.