I worked briefly on a Gartner (and Forrester) pitch for a services company. They do do an evaluation and you get to make your case. We had to compile case studies, highlight our competencies and the like. Put it in a deck and present it. Then they call up our references and get their input. We even had a consultant who specializes in helping companies with their rankings. As a services company, it was pretty similar to how we pitched clients and I gather the evaluation they did was also similar. I didn't get any hint of corruption in the process but I wasn't really in position to see it if it were happening. The execs seemed to take it seriously and put sincere effort into it.

I was aware of years ago parallel Forrester and Gartner evaluations of a new product my company was building. Forrester went through it in detail, even measuring number of clicks to access features and so forth. Gartner just did it all based on existing company reputation.