in (all) conscience
Without guilt. Usually said to emphasize fairness in a transaction. Primarily heard in UK. In all conscience, I can't charge you more than the car is worth. No, I can't, in conscience, give you a better grade when you put such little effort into the assignment!
in conscience
Also, in all good conscience. In all truth or fairness, as in I can't in conscience say that the meeting went well, or In all good conscience we can't support their stand on disarmament. [Late 1500s]
in (all good) conscience
In all fairness; by any reasonable standard.