You can't with the sophisticated ones. You test them. Not just with one test and not within a limited amount of time. Users are within your own family who you have not come to know until years of after thought.
This post was edited by O-uknow at December 14, 2017 9:27 PM MST
I'm not an authority on that but I know test them you must, over time. One test I would use that I didn't see on the net is see how they handle failure to deliver on what they expect. Do they stick around or do they depart.
This post was edited by O-uknow at December 14, 2017 9:27 PM MST