The following information is from Google.

"SEO is an acronym for "search engine optimization" or "search engine  optimizer." Deciding to hire an SEO is a big decision that can potentially  improve your site and save time, but you can also risk damage to your site and  reputation. Make sure to research the potential advantages as well as the damage that an irresponsible SEO can do to your site. Many SEOs and other agencies and consultants provide useful services for website owners, including:

    Review of your site content or structure
    Technical advice on website development: for example, hosting, redirects, error pages, use of JavaScript
    Content development
    Management of online business development campaigns
    Keyword research
    SEO training
    Expertise in specific markets and geographies.

Keep in mind that the Google search results page includes organic search results and often paid advertisement denoted by the heading "Sponsored Links") as well. Advertising with Google won't have any effect on your site's presence in our search results. Google never accepts money to include or rank sites in our search results, and it costs nothing to appear in our organic search results."

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