What could cause my rc car to not go in reverse?

This isn't the first time this happened. I've been able to narrow down some things. I've tested the motor and that was ok. It goes forward, but not reverse. I'm thinking that it's the controller because I think it's been used. I found one online and noticed it had stickers missing, so that's what made me think it's a controller issue. I plan to try new batteries first to see if that fixes it. It's done this before and fixed itself. But, I'll try batteries first and see what happens. Still, I think this was a used controller.