Buying used Audi... Should low price set off alarm bells?

[w_alloy]

I need a new car, and found a used 1999 Audi A8 Quattro with 102,000 miles in "immaculate" condition for 5k. The book for one of these with this amount of miles in "good" condition from a private seller is around 16k. It looks like a great car.

I talked to the seller and he said he buys and sells a lot of used cars, and this one he got from a friend in a different state for 4200. He said he re-painted it and cleaned it up a lot, and it runs perfectly. I jokingly asked if he stole it over the phone and he kind of nervously laughed (maybe it was a normal laugh, it was over the phone and he I've never met the guy). The price being this low worried me. He seemed like a nice guy in his mid-late 20s. I am going to see the car tomorrow.

I have no experience with cars, especially buying them. I have a few questions: Is this low of pricing normal? Is this a good car; does anyone have experience with it? Should I get a mechanic to look at it before I buy? I was gonna do a car fax report, but realized I needed information I didnt have. Should I get the car's number and do one before I buy? If it actually is stolen (which I think is a long-shot btw) is there any reason, moral concerns aside, I shouldnt buy it? With a deal like this, should I act fast so noone else can snatch it from under me? Anything else I should know?

Sorry for the semi-long and boring post but I've never bought a car before and could really use this info before tomorrow.