Here is a video demo of how to check for an impact crack.  Sometimes the crack is not even visible, but you can always hear it.  Definitely do this when your pot arrives to make sure that your new pot's trip from our house to yours wasn't  too interesting!  We highly recommend that you perform this test over your sofa or a bed.  It would be a bit tragic to drop and break something while checking to make sure it's okay!

The first pot in each example is undamaged and the second one has an impact crack from an accident.
(We get hasty now and then.)