I'm pretty new to the PHX area, and not a master of TDI's by any means, however one of the biggest piece of advice I've learned about TDI's is learn about it's timing belt history. If it's 60+k miles (Depending on motor and OEM TB mileage rating) find out everything you can about the TB on the car, including where it was done, what parts were put on, and get receipts, if they did it themselves ask lots of questions like did they use a Vagcom to finish the job, how did they find TDC etc.
If the previous owner can't supply that information in a satisfactory way add 500-1000 to the purchase price to get it done ASAP *(Not sure how much a tb job costs out here, I got mine done in NY)
You may also want to check the trusted mechanics list and get in touch with them, they may have a car on the lot. (I haven't worked with any of them)
http://forums.tdiclub.com/showthread.php?t=130044
