I had a few bad experiences when i used to live in the states several years ago.
-they never knock (will leave your livestock in the heat/or cold) even if you have your door wide open, with a big sign indicating for them to ring the door bell/or knock and come in because you have expensive products. Most of the time, they run up toss the box down and flee away. I have watched from my window before where they did this. (of course i had my digital camera) and a complaint was made to their supervisor.
-deliveries that were supposed to made at a certain time, was late/or delayed. When you pay for a service, you should be able to get it.. if they claim to be here by 1030hours and show up at 2pm, i should never be charged for the price.
-sometimes they were spot on, other times they fell off the deep end.