A surge of impostor scams targeting US casinos has been warned against by tribal gambling operators. The National Indian Gaming Commission urged operators and regulators to be on the lookout for con artists posing as vendors or state or tribal authorities attempting to defraud casinos of sizable sums of money in the letter it delivered to the tribal gaming industry this week. The announcement comes after reports that a man was detained last month on suspicion of stealing $1.17 million from Circa in downtown Las Vegas while posing as the casino's proprietors.