How about honesty or truth. Seems funny that these types of relationships demand open, (radically ) honest communication but the break ups not so much. It also seems backwards that people would start lying on the way out the door. I would think the demand for honest would be the same....during and ending.
In a good break up I'd look for the truth.
Depending on how the break ups happen it says a lot about ones character. Some people are gutless ...don't want to be seen as mean, etc, etc.
If you could see a long pattern of shitty break up you might want to weigh that going in otherwise it might be unfair to judge not having been in the relationship...easy to Monday morning quarterback.