Wait -- what? They actually
did put the trip odometer on the sales contract, and not the actual mileage? Did they also falsify the odometer statement, or was this just a misunderstanding based on not reading all of the documentation they provided?
If that is really what happened, than I'd say you have a very strong case for returning that vehicle for (at the
very least) a full refund. Honest mistake by a newbie salesperson? I doubt that very, very much. There's a certain level of basis competency that one has to be able to expect from a car dealer. There is NO way they didn't know the actual mileage. You're dealing with a car dealer that has already tried and succeeded in cheating you. No way of knowing what else is wrong with the vehicle, but you should know by now that you can't believe a word they say.
If I were in your shoes, that vehicle would be gone in a heartbeat, and I'd be looking for a different one... from a different dealer. If the one you bought from balks at taking it back, remind them that there's a federal law that provides for a $10K fine, plus you can file a civil suit.
49 U.S. Code § 32705 - Disclosure requirements on transfer of motor vehicles | U.S. Code | US Law | LII / Legal Information Institute (cornell.edu)
49 U.S. Code § 32709 - Penalties and enforcement | U.S. Code | US Law | LII / Legal Information Institute (cornell.edu)