If you don't knock they may not hand it over , id knock and stare them in the face and say there is an ongoing investigation of who delivered what to where , it happened to me when a delivery was made 4 doors down , the chap four doors down just a number wrong 14 v 4 my name it , he knew me had it for a week knew it until I stared at him he was never going to hand it back , went all apologetic on me , I took the item off him , gave him a **** you that not your name , and left