Look through the stickies and find the car you want that cannot be treded. Check what ticket it comes from and trade for that ticket, Dupe it to another account resend and cycle ticket till you get the car you want.
From memory there are very few cars you cannot dupe or get from tickets X2010 to start with but you get the vetel for reaching B-spec 35 and you can buy any painted one at level 40, unfortunately to get a raw carbon you have to gold the vetel challenge.
What car are you after.