Power trip. That's what it is when a player does this; that's what it always is when a munchkin is involved. Munchkins get off on power trips, and on having the most powerful character who can do anything he wants (especially if it means stomping all over the game world doing things like fighting gods toe-to-toe and winning).You could, but why would you want to? What does that prove?
Play style clash, as I said above.
Correct! As a GM, you have to be able and willing to fulfill the role implied by the second word in the acronym: in other words you must be the game's master. It's great to give the players free choice, and every good GM does so as often as possible, but you must also know when to step in and tell them "no." You must be a judge of their actions; it's part of the job of GM. And if a player does cheat, you have to be ready and willing to call him or her on it.Usually my approach is to ask the players to look up the rules if they appear unusual or unbalanced. I'm a fairly trusting DM and like to keep the game moving quickly. I guess it comes down to identifying the players that are and aren't trustworthy.