These engines are not that tough when boosted to much, way too many posts about pistons letting go and cracked cylinder towers. Yeah, they will make 300 HP for 20-30K miles but beyond that it's a total crap shoot.
I don't like the fact that the car in question had an aftermarket BOV. Come on, without a lot of other parts and work that BOV does nothing for the power. IMO it's a really safe bet that the previous owner had a higher capacity turbo on the car and was probably making 300 or more HP. I would not touch this car with a 10 foot pole. So, take it back.