Do You Recommend A Comprehensive Duplicate Content Checklist Or Outsource Service?

In episode 98 of our weekly Hump Day Hangouts, one participant asked about having a comprehensive duplicate content checklist.
The exact question was:
Have a potential client who appears pretty competent at their own SEO, but by no means a power user. He has great Maps rankings, awful organic, claims it’s from Penguin update 2 years ago. Claims to have been diligent in link disavowal, dupe content deletion…
Assuming that is all true, do you recommend a comprehensive dupe content checklist or a service I can outsource to?
