Personally, since I've been in this exact position before, I'd prefer a face to face chat about why packages are getting damaged. Most people are pretty cool if you are cool to them. If it escalates, and I get threatened or yelled at, I leave and I take the package with me. Now they get to come pick it up themselves. I also would never go back after being threatened. They would have to come pick up every package they get. Basically, don't go threatening people who most likely didn't do anything wrong, it'll only make things worse.