I have 365,000 miles on my V10, all original except radiator, and it still runs great! It's not a MH, but about 200,000 of those miles are towing miles and typical combined weight is 22,000 pounds.
That said.... that many miles that fast probably means it was a rental, which means its been used by a lot of people that have no idea how to care for an RV. Check everything carefully. Things like the fridge being out of level or not using a pressure regulator are just a couple example of mistakes renters may make.