Along with everything thats been mention, always should get the car checked out by a mechanic that you trust before you hand over the cash, because that way, even if you think the car is all good and clean, a experienced mechanic can tell you exactly what sort of condition the car is in.
But to be honest, I think buying a R34 GTT off a dealer is a bit of a rip.... They all put up the price and over charges everyone ($20,000-$25,000).
I think it's better off buying it privately, but just make sure you get the car checked out before you buy it. That way, you might save yourself a few grand. I just bought my manual GTT for $16,500 on the road off carsales, its got 105,000km on the clock, but the condition its in, is immaculate, its so good that the seller even serviced the car with nissan lol