Law Firm Wanting To Increase Leads Through SEO

I've recently joined my firm and was shocked to see how few potential clients were visiting our multiple sites. Now, we practice a few different areas of law and for some of our niches, one client can very easily mean +100k in revenue for us.

I've started doing keyword research and know our few competitors so I can see what keywords they are doing well on. I've also bought backlinks and have seen our traffic triple over the past few months, but I know we could do so much more.

There are thousands that claim they are SEO experts. What should I look for in hiring a consultant or professional? Of course, not all "experts" are the same.