Go into your garage, Hit LB or Q to go to the crew garage/showcase, Press X on XBOX/PC or square on PS4 to change the crew garage into your personal garage then select the car(s) you want to sell.
Hope this helps 🙂
Hello,
I had the same issue and I just wanted to give my experience on this. I am using PC.
When you go to the showcase, select the car (on PC click Enter). It will select the car and give you few options one of them is to sell the car or swap its place in the showcase with another car. When you swap it, you can sell it.
For the starting car, you cannot sell it. Also for some other cars when you sell them, they sell for 0 so you can sell them and buy them again and have as many copies of them as you want because they sell/buy for 0.
