Very good condition..but it's got 88,000 miles on it. The color is blue w/ blue suede/black leather interior. I checked carfax...the car had no problems in the past. Is $13,000 reasonable? Or, it's not worth it? Will the maintance be too much? I've never own an Audi before...

Sounds like a good price for the milage on it, but beware!! Audi parts are veeeeeeeeeeeeery expensive, and most of the times you have to order them directly from the dealer. Remember used cars always have little details that you must keep up with, so if you are willing to pay a pretty penny for parts, go ahead!

well first of all there are lots of places to get Audi part other than from the dealer I've owned three and can count on one hand the number of times i've been to a dealer. There are lots of internet sites and even local auto stores that carry most parts. secound of all the S4 is the sport model of the A4 and it is a tuned up engine that will require more maintenance than a regular A4 engine so if you are just looking for a nice luxury car than look for an A4 if you want the extra power and handling of the S4 then yes this is a decent price and this car will perform well. there are very few comparable cars out there when you look at the whole package you are getting.
The A4 is one of the most reliable German luxury cars the S4 is a little less reliable but by no means bad but when you tune up the car and drive them as hard as most S cars are driven reliability takes a hit.