Precautions: 1, check the shell surface is smooth and no scars; 2, check the box is not rough edges and corners, if there is aluminum angle, but also check whether the package is solid; 3, took the box a few steps, take a look at the bottom wheel is flexible, steering ability is not strong, the wheel is very important, you should choose multiple rows of wheels and rubber wheels; 4, press the button, pull out the lever to see if the retractable, functional intact; 5, if it is hard box, you can put the box flat, put a heavy object on the box, you can also stand on the box, the quality of the box is absolutely no problem; 6, the most important thing is to check the performance of the lock, if you have a password lock, you can feel free to adjust a password try it, but to note that in the official tune password must choose to facilitate their own memory but not easily forgotten 3 digits .