Let me tell you a short story. Three years ago a friend had a Medical Extension done by an "Agent"... He went into the local Immigration Office at one point. The I/O at the Front Desk looked at his passport as said "This is FAKE" we know who processes these. She stamped it as bogus (using Thai Immigration terminology). Then put in a stamp that he had 7 days to leave Thailand.
So go ahead and pay tens of thousands of Baht - let the Agent have some fake or bribed doctor sign the Medical Extension (as he does for many others - becoming well known to Thai Immigration). Then if you are lucky you will get only a 7 day stamp to leave Thailand... (but better than being put in jail for Immigration fraud).
He will lose. It is simply a waste of time. There is way too much evidence that China is at the heart of this Fiasco. This fellow has been reading too many conspiracy theories