MageHunter wrote:...1st level campaign where the GM would threaten to send a Froghemoth after us. I normally use Tarrasques.
Make it doubly memorable by delivering the Tarrasque through orbital insertion.
What I find particularly ludicrous about the player's excuse is that it's really, really uncommon for a group of PCs to achieve 100% treasure recovery on a dungeon. People miss rooms, overlook hidden compartments, monsters run away. If I were trying to 'help' or 'make things easy' I'd definitely keep a loot list, but I wouldn't be downloading any files to make sure 'the GM didn't forget any loot'.
I suppose you could apologize to the honest players, explain the next two adventures will have no treasure at all, and explain that you're just following wealth-by-level guidelines after Player A 'made a clerical error', but why pussyfoot around? Tell him he didn't 'help', and if he wants to 'help' and stay in the group he'll delete this bogus list and employ the list of items legitimately acquired. Which is a shame because he won't get to include the twin sun blades you had tucked in an extra, unofficial room.
Eh we honestly have no idea what's going on based on the OP's statements the player made a loot list including all the loot from the AP and claims it was permitted but we don't necessarily know what that list was for. For example this could have easily been a preliminary step to printing out loot flashcards so that the DM could hand them out whenever they were found. Alternatively he could have been trying to check to see what the players had found vs what they had bought because of how the party dealt with loot splitting when they sell items. This issue could have much more to it than we know based on the tiny bit of information we received.
Was this his personal inventory list that magically sprouted new items they never found or is the cheating in question just him having foreknowledge of the AP because he looked through the AP to write up a loot list?
Mind you, you still run into the guy having read the AP issue but that's not really a huge deal since there are plenty of times you have a player who's either played or GM'd an AP before and knows more than they ought to.
As far as how you deal with it I personally think that just following an AP straight out of the book is always a bad call. It's the easiest way to GM but it means the encounters are always balanced wrong for your party, the loot may or may not be any good for them, there could be roleplaying problems that shouldn't come up if you built the encounters, and you run into cheating/knowledge issues like this.