Seeking practical SEO advice for a newbie

I hired someone to do build a site and do SEO for my small service-oriented business, but I have the feeling he's not shooting me straight. My site has a ton of content, way more than any of my customers would ever read, I think I have upwards of 500 pages on my site, and I can't understand the value in the reports he sends. Are there some basic questions I should be asking to make sure I'm not getting ripped off?