To be honest i have no idea why you went to a dealer in the first place there are a lot of well maintained skylines being sold for a similar price under the sales section of the forum i would have personally started there or on carsales i believe Private sales are better for second hard cars than dealers. Some good points made by the previous posts above though! imo i wouldn't buy it, search for another one im sure you can find a much nicer much cleaner one on here or carsales.
Edit: My bad just saw you where new on here just thought id give you my opinion Also check the reg / vin with your transport authority (e.g. Vic Roads) they can normally tell you a lot about the car stolen history, damage history, finance etc...