This, while true, is all moot in this instance. Unless the source knew a) exactly what Gogerty Marriott was engaged to do for Curt Knox, under what terms, and with what level of staff/time commitment, and/or b) what actual sum of money was paid by Curt Knox to GM/Marriott, then the source is worthless in any case.
It's meaningless to say that GM's fees are "around $100,000 per year". For one thing, GM does different things for different clients, with differing levels of staff, time and expertise commitment. One could hire GM to do not very much over the course of a year, and perhaps pay $25,000 in fees. Or one could hire GM to commit a sizeable chunk of its manpower and expertise commitment on a daily basis, and perhaps pay $300,000 in fees. And for another thing, GM very probably charges different types of client different fee ranges. In fact, in a case such as that required by Curt Knox, it's not at all improbable that GM took the project on at either a substantially reduced fee scale, or even pro bono.
We also have zero proper evidence of what exactly GM did for Curt Knox, in terms of the level of commitment of manpower, expertise and time. The best evidence we currently have is in the form of statements made by both David Marriott and Curt Knox, in which both men imply that GM was hired to manage media relations and to manage the story that was being given to the media. And there is zero current reason to believe that GM's role went any deeper or broader than that - which also would mean that GM only performed a very limited range of services for Curt Knox, with a very low investment of manpower, expertise and time.
So, forget all about this "$100,000 per year". It's meaningless in and of itself, and it's doubly meaningless in the context of the Knox case.