Purchase advice Phaeton 3.0 Tdi 2007

Hello Phaeton driver, I was looking for a solid long-haul vehicle, which also makes 400km at night in 2:30. I stepped on the Phaeton. I know this upper class is quite good and cheap. I found this one in my surroundings, which I really like very much.http://home.mobile.de/AH-ROELL#des_181379736 I wrote to the dealer, and he offers me the Phaeton for 16000 but without guarantee! But since I buy privately, he has to give me a guarantee, or am I misinformed there!? He will not give me a letter when I buy it where I don’t like the guarantee or!? Warranty would be important to me, because I had 2 used by Private in the last 4 months, and now both are there. The last one is an Opel signum, which has a low-bay sink, I lose coolness if I have about 140 km/h and from about 40 km. What do you know about it?