If you are selling products on your website you have much different needs than a locally focused business. You need optimization not only for your category but for the individual products you sell.
As Google has become more and more technical, technical acuity is more important in the SEO company that you choose. We have been doing SEO for eCommerce sites for over a decade and have helped sites grow by several thousand percent in sales. We have also rescued sites that had previously enjoyed high rankings in earlier years but find themselves having dropped into oblivion or in the process of doing so.