As a general rule, people who call you trying to sell you something aren't doing it to help the person they're calling. Anyone who sells on eBay already has some SEO skills, they may just not know it yet (it is generally about effective, click-worthy content, so your experience with writing titles and descriptions gives you a headstart).

I would start with some general research - there is a lot of information about SEO, but you can start with the basics so that if you decide to go with a consultant etc, you'll know what you're need from them rather than have them tell you what you need (and how much it'll cost!) - here's a decent overview with some tips: http://blog.kissmetrics.com/simple-guide-to-seo/