This happened yesterday to one of our clients. A customer had an order that was delivered a few days ago. Yesterday the customer rings up to say that they are still waiting for the goods. The retailer did some checking and was assured by the delivery person that he did deliver it, it was to the right address and it was left on the side of the house as requested. The customer is saying that they never got it. Maybe they are both telling the truth, perhaps not but how does the retailer prove that the goods were delivered.
My advice make sure you get proof of delivery.
Now with the higher stress on delivery currently in retail, I am sure this problem will get more serious.