We just fired our last GM for cheating. How can a GM cheat? The same way he cheats as a player. He almost never has his character sheet. When he GMs he has some things written down, but often the monsters are not written down - nor are the Saving throws. So when we attack or cast spells on his monsters, they seem to make their saves always and the saves seem to vary. This GM has favorite players allowing some to hit with a low roll and others to miss with a high roll. If you corner the GM with the knowledge that he doesn't have stats laid out - he'll tell you its in his head.
That's not cheating, according to the 3.5 DMG and other sources on DMing.
You may not like his play style, but he's not "cheating". He's running the game in a manner that you don't like.
One of the most fun games I've ever had as a player was a Classic Traveller game run by a gifted GM who made up everything on the spot.
Now, D&D is a different game, and the GM you mention runs his game more Old School style. I'm not sure I'd like the way he's does it, either. But, I wouldn't call him a cheat.
As GM, it's his world. He can mix, change, bend things to his liking.
Where he's failing is that his players aren't having fun. And, that's a pretty big failure as a GM.
But, he's not cheating.
I disagree. While I am aware that some groups are ok with some amount of fudging on the GM's part, I would disagree with the idea that the GM cannot cheat.
Check out page 18 of the 3.5 DMG. Top right hand side of the page discusses "fudging".
The cardinal rule with fudging, mention on that page (and something I agree with) is to never let the players catch you doing that. They'll lose faith in your GMing abilities.
During an encounter, if the GM (without some really good story reasons why, and even then it would be suspect) starts rolling d30s for the enemy's longsword damage, I would say that is far beyond 'fudging' and quite possibly enters into 'cheating.' Likewise, if the GM declares "you all die right now because I say so; rules be damned," I'm inclined to view that as cheating. At best, I'm inclined to no longer be a player in said GM's game.
Agreed about not playing in that GM's game.
Again, he's failing at the "fun" part, but he's not cheating.
Giving a few men-at-arms longswords that do d30 damage or fighting a huge number of Orcs all at once--it's the same thing. The GM controls it.
You can't call one thing cheating and the other not cheating.
The GM can do things you don't like. And, you can set up House Rules to help "govern" your GM. But, in the end, when you sit down to play, you agree that one person will be the absolute authority on the game. And, that person is the GM.
With that kind of authority and power over the game, he cannot cheat.
He can do things you don't like. And, you can decide not to play with him.
A smart GM won't do those things (or let you know that he's doing those things), because the GM's number one job is to make sure everybody has fun. If his players think he is "cheating", even though it's impossible for him to cheat, then the GM is failing at his job.
If it's your opinion that GMs cannot cheat, fine, but comparing such an idea to an 'established fact' is (in my own opinion) not a valid comparison.
The GM being unable to cheat is fact, not just my opinion. I've listed examples. I've pointed to a page in the rule book that says the same thing. I've provided more support to back up that fact than anybody else has when saying that a GM can cheat.