Aaah, Returns!

This man came into my store this morning looking for a box to pack a guitar amplifier he sold on Ebay. Using all 6 years of my wonderful UPS experience, I recommended a box to him, and even suggested how he should pack it to make sure it gets delivered safely (in one piece). Later that afternoon, he brings the box BACK and says its too big and asks to return it. However, it looked like it had already been shipped FIVE times and I asked what he did to the box?? He said it got rained on. I apologized and told him I could not return the box in its condition. Furious, he started accusing me that I sold him a box too big on purpose and owe him his money for a box! ... What?!