I'll just bump the car a year newer... it'll reflect 6 months decently, especially since 6 months ago was still in last model year.
Well, you're in an area that likes Contours... the Regional adjustment difference was +$170 between Florida and Washington.
Making the same assumptions I made in the first case (everything but ABS and traction control)... assuming "clean" condition.
Dealer: $1963
Private Party: $2842
Dealer: $4180
Given the sales channel and geographical location, I think you two did equally well. You got $558 more, he got the necessary repairs which would have eaten his private sale advantage away and then some.
Keep in mind trade-ins reduce the amount of sales tax you need to pay in most states, as you are vendor selling part of the value.