The only time i touched competitors packages was on a letterbox route. 15 letterboxes a night id always find some mail and a fedex or dhl letter or package. My last letterbox in a big office tower had a ups, fedex, dhl, and mail drop all next to each other and id dump the stuff that was in my boxes each night.
Unavoidable and managment knew i had to do it each night. Taking a competitors package and delivering it? Thats a different game you can and should be fired for that.
I know of a driver that was fired for handing out adverts for his side business as he was delivering. Was warned (suspension)about it and he kept doing it anyway and the termination was not overturned