If you have received spam email offering you SEO, ignore it completely. Anyone who contacts you randomly via email offering to rebuild your site for $299 is a charlatan.
There are certainly things that you can do to a website to improve its search ranking. I had a website where all the urls were grabbing data from a database. For example, if we had a page about something stored as record #1234 in our database--let's call it Flibberty Gidget Widgets--then our site originally had a url like http://example.com/pg1.php?id=1234. This url did not rank well at all.
Through a herculean effort, we created some fairly complicated server arrangements so that our site hosted that content as http://example.com/flibberty-gidget-widgets/description-1234.html and our search engine ranking dramatically improved. We also made sure that the <title> on the page and meta description also said Flibberty Gidget Widgets and that there was a <h1> tag on the page that also contained this text.
It's worth noting that our search engine ranking suffered temporarily as all the old urls got dropped before the new page urls were crawled. Part of our herculean effort was to 301-redirect the old urls to their new counterpart. We managed to get the Google top 3 for a very common phrase, "highest paying careers." We've since slipped a few notches because our site is not mobile-friendly.
To do SEO properly, you should target the exact phrase you want with no extraneous words. Use dashes instead of underscores. Make sure your site is mobile-friendly. Make sure you don't spread your page popularity among many different pages with slightly different wording. You should have one page that targets the search phrase that you want.
Buying ads may also help, but I know little about how that works. Search engines are complex. It is said the Google search results are dependent on some 200 data points, many of which are supposedly specific to individual users. Your search results are not the same as mine.
