Take this example. A seller sends an item with no insurance. The item is lost in the mail. The buyer says to the seller "You didn't send my item, I want a refund." The seller says to the buyer "I sent your item so I don't owe you a refund." Neither party could prove to the other what took place. How could they resolve this matter? The seller would think that the buyer is trying to rip him off and vice versa.