We had a major scandal over grade changes of this sort at my university about five years ago. The guilty parties were in the Registrar's Office, and would change grades for a fee of several hundred to over a thousand dollars. All of them were fined and received prison sentences, which was what they deserved. Two of the three involved were graduates of the same university.
Strangely, the guy they called the ringleader changed his grade in my Spanish class from a D to a B+ rather than an A. I guess he was not that confident that he could be taken seriously with an A.