Action Line: Protect yourself when buying a used car

Dear Action Line, I just bought a used car. It was the worst experience of my life. I traded in my old car. Now, they told me my credit was denied. I just want to give the car I bought back and get my old one returned.

The dealer told me I could not cancel. I didn't even sign the pink slip from my car, so can they sell it? What can I do?