Thanks guys for responding.
Here's the deal..
The buyer left a deposit. He will be sending a transporter to pick up the car this coming Tuesday along with the balance of payment.
As I mentioned before, we agreed on $15k. This was before I did any market research on the fair value of these cars.
The last couple of days, I've had some time to surf online to see the fair market values and was surprised at how much these cars are going for. In light of this information and from your feedbacks, I am considering calling the buyer for renegotiation to a more fairer transaction.
1983 911sc
169300 miles
Upgrades:
1. New rebuilt transmission and clutch February 2014
2. New fuel pump January 2015
3. valve adjustment w/new valve cover and seals
4. generator 2 years old
5. replaced old bosch cd unit with permatune December 2013
6. New Bridgestone Potenza tires. July 2014
7. replaced leaking thermostat sensor when transmission replaced
Need Attention:
1. Driver's side window not working (may need new regulator) window motor is fine.
2. Sunroof left side cable need replacement.
3. AC needs attention (o rings replacement) compressor is ok.
4. Paint look good on the pics but closer inspection will show rock chips in front, a scratch on the right passenger rear fender. Paint bubble on the left rear side panel about 1.5" in diameter (a little rust spot)
5. Driver's side seat ripped. definitely needs reupholstery.
Other details:
The motor is strong and sound. This car has been my daily driver and is very dependable.
Discovered later after I purchased in 2005, The car has been in an accident, I know now that the drivers side door has been replaced and the car has been repainted at least once. In light of this accident, The car rides straight and true. It has a clean title.
Since I have a couple of days before the transaction if final, I'm looking for more feedback from you to help me decide whether to renegotiate or not.
Here are some photos of the car:


Thank you in advance for your feedbacks.
Carl