No flips for you!
I ran almost this exact thing in one of my games, only instead of locals is was a secret society of knowledge seekers and instead of treasure it was ancient arcane secrets. The PCs managed to turn it on it's head and force the society agent to flee while the orcs allowed the PCs access to the ruin in return for revealing the betrayal. Of course, the orcs also immediately started making wagers among themselves as to which orc would be brave enough to venture into the ruins to retrieve the loot from the bodies of the PCs, so not all sweet and lightness.Small kingdom (or province, or whatever) is suffer depredations by a tribe of orcs from the nearby mountains. The orcs are pretty vicious, and have slaughtered a lot of farmers and even completely wiped out a small village. Those they don't kill they take as slaves.
Heroes get to have fun killing orcs for a while, going off on various missions and being richly rewarded by the nobles for their efforts.
But, over time what they discover is that the nobles are secretly in league with (insert bandits or drow or drug dealers or Nazis or something) and have been provoking the orcs, and committing their own atrocities against them. The nobles have learned there is an ancient tomb, potentially stuffed to the gills with treasure, right smack dab in the orcs' stronghold, so they are hoping to motivate the populace to go to war and wipe out the orcs.
AWAB?Aren’t the Watch classically pretty Good and not corrupt, in Waterdeep?