As others have said, you should get a detailed list of what SEO services are being performed on a monthly basis. Is he writing blogs? Is he getting you back links? Is he optimizing you’re inner pages with rich keyword copy? There’s probably over a hundred things they could be doing. Or they could be doing one thing poorly and charging you $600/month because you don’t know any better. If he’s doing everything RIGHT it usually takes about 6 months to see a change, but that change doesn’t mean #1 on Google.

If you’re a service based business, I would check out local business ads on Google. I believe their Pay Per Lead, not Pay Per Click. I would also focus on optimizing your Google My Business. That ranks much faster and you show up on Maps pretty high.