A lot of the shill marketing is very hard to prove. A lot of the dialogue gets mixed in with commentors that have genuine brand loyalty.
It's far too easy for a marketing team to acquire a high karma account and blend in. We'll never get a truly clear picture of how much Reddit is astroturfed.
I replaced all my comments with the same phrase before deleting them with PowerDeleteSuite. The comments were fully restored and visible through a google search (but not visible through the user page). My posts were not restored, AFAIK.
This was during the whole 3rd party API thing. Maybe it was just something done during that time, but they certainly got around the edit replacement trick before.