I test drove this vehicle and when i got to about 60+ mph the engine begin to skip and shake some.
The dealer put the car in the shop and he said there was a spark plug with a hairline crack in it and that was the problem. Before I buy the vehicle, could this be true?

By the way, it is a 97 Mazda Millenia. I selected 929 b/c there was no other option close to the Millenia.