For This 5 location optometry group we took over an existing AdWords effort, and was able to quickly tighten up campaign efficiency, dropping CPC rates in half, and exponentially increasing conversions (calls and online bookings).
At one point our client was solicited by a jack of all trades web company that promised to do great PPC work. So our client left us, but returned after a few months after results plummeted. When they returned, we were able to optimize for even more conversions. Heck, everyone makes mistakes!