World Of Books review: Books being sent to you are not being received

There have been several instances recently of books we have sent to and you have claimed the books were not received. The most recent was today on trade 11662014 where 15 out of 20 books were "not received". As the person who packed them, this is nonsense. Do you have video checks of when boxes are opened by your staff? The weight of the box we sent must be in the system somewhere and how does this compare to a box with only 5 books?
This issue is occurring more and more and we noticed that it mainly occurs with high-value books (there was a book valued by you at £47 recently which was "not received"). Can you please explain what is going on and how you control the receipt of book?