First of all its a dealer so they need to get there cut above what they got it for. Private sale would equate to mid $6k-$7K(ish). Tell them to fix the air and the brakes and offer $8K as long as the paint could be compounded out(most likely). 100K miles is 1/3 of the lifespan from what I've heard of people(as long as maintaince an moderate repairs are figured in accordingly).