"Benefit of the doubt" is a standard phrase in English and is a very useful one in formal discussions. Is there an equivalent expression to denote the opposite of it, formal or informal?
Sara: What do you think of our new neighbour?
Sam: I do not know them, but I'll give them the benefit of the doubt. [they must be good people]
How about an opposite case (I will try to convey it below):
Sara: Will you marry me?
Sam: I do not know you, so I have to __ (I wont risk it, you could be terrible...)
One thing I can think of is possible risk. Is that how the English speaking world go about this?