The direct method is to check whether there is any damage to the frame and other parts. Usually it is a frontal impact. Look at the steering part. If you have good skills, you can loosen it while riding. Check the handlebars to see if the vehicle is running in a straight line. If there is a serious deviation, it means there is a serious problem. If there is a slight deviation, it means that the vehicle has been dropped, but it is very dangerous. It is not recommended that you try it. It is better to observe carefully with your eyes to see if there is any plastic surgery or Welding~~Because the welding parts of the vehicles produced by the original factory are relatively regular~~