It might be worth running a vehicle check now to see if there is anything of note there. If it shows a mileage discrepancy, then, it probably strengthens your argument in discussing with the dealer. They may say that you should have done a check yourself, but as a consumer you should be able to make a case that they are professionals and have a higher duty of care, and should reasonably have known.

In reality, they’ll probably fob you off, and unless you’re prepared to go the small claims route then it may just have to be chalked up to experience, and take the hit. Sorry!