Original 12.8mp 5d thoughts.

KEH.com is my go-to place for used gear.

As far as what to look for, there was an issue with the adhesive holding the mirror on failing and dropping the mirror.  Make sure this has been fixed.  We had both of our shutters fail at about 200,000 clicks, so make sure the one you buy isn't over-used.  (When the shutter failed on my wife's camera, it scratched the sensor...not a good thing.)

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Skip M
www.shadowcatcherimagery.com
www.pbase.com/skipm
http://skipm.smugmug.com/
http://skipmiddletonglamourshooter.blogspot.com/
'Living in the heart of a dream, in the Promised Land!'
John Stewart