Nope.
Unless the salesman put his mileage claim in writing, in very specific conditions (extremely unlikely), you have no recourse.
Mileage claims, like most other 'puff' sales tactics', have little basis in fact and are considered just that.... PUFF.
How many times have you heard a car described as "in cherry condition" or "excellent shape". These, like the mileage claim, are self-serving claims without any substantial basis in fact.
Hell, he could legally claim that you CAN get unlimited mileage... you just have to drive downhill all the time...
Kind of like the "all you can eat" buffet... they don't tell you that it has to eaten while in the restaurant or in one sitting.. and no, you can't come back tomorrow for free seconds!!!!