Some of it is not really common sense, because people make these mistakes all the time. I suspect the main mistake he has made, and this happens very often, is that in order to get a decent margin on his product he had to order a fairly large quantity. This broke two things, one not being able to test out the product to determine if that is what the market wants, the other is not to get the hang of all the things that can go wrong with importing goods. I think he was particularly lucky to get it through customs so quickly.