First, you should check if it's an old bike or not. When you are checking for a newer model, you should check for the name of the manufacturer on the frame. Next, you should start with the frame, checking for scratches on the frame near the wheels. If it's an older bike, you should check the engine for any signs of tampering. If it is a newer bike, you should check the engine for oil leaks or anything that might have been tampered with. Additionally, you should look into the saddlebag for anything that was put in there. Lastly, if it's an older bike, you should look for the VIN number on the frame near the frame's engine