I put a car up for auction while I was at work, just got home now and saw that it sold. Why didn't I get this achievement? Do you have to stay online to get this achievement?
It's a while since I got this one (or even sold a car) but don't you have to send the car off to the person who purchased it to get the achievement?
You just go into the auction house and under the tab my auctions you see your auction and it says sold. Enter the finished auction and click on receive credits after that you will get the CR and the achievment i just got mine ;)