Great question — answering as the UphillTech team:
There aren't sites or plugins that "[maintain] good SEO for a Wordpress site representing local business." Instead, there are good SEO plugins and good SEO service providers and good SEO education sites that give you the tools and education to target your site properly. There is also no verification process aside from popularity and survivability. Search for SEO plugins at the WordPress.org repository and look to see which ones have been downloaded the most and rated highest.
Full answer by JCL1178: https://webmasters.stackexchange.com/a/42536 (CC BY-SA 4.0).
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