Tony,
It may be a legitmate question, or just muck raking with little or no basis.
I can recall two or three press documented instances since 1977 when I entered the business of gca's being involved in dishonest behavior. As I tried to say before, its such a small industry we usually here whispers about this or that. Its hard to believe that you apparently hear a lot more about that kind of thing than I have.
Frankly, I can't recall hearing any of that, so I suspect its not common, especially among the well know gca's who are already compensated handsomely for their work by clients. If you are getting a million dollar design fee, or even half a mil, how much of a payback would you need to get to make the possible disgrace worth your while?
I tend to agree that we should be careful with this topic. By and large the industry is full of good people, and the suggestion of such tarnishes the whole bunch to a degree for no good reason.