There are a lot of Christians out there who say that 100% acccuracy isn't necessary for a true prophet. They'll say that even a true prophet will sometimes get things wrong. They'll be mistaken at least part of the time. Giving false prophecies does not, necessarily, make somebody a false prophet. I want to mention a few reasons for why I have a hard time accepting that.
First, what is a false prophet if not somebody who gives false prophecies? I wonder if there's a scale or something. Maybe if you get 50% or more right, and the rest wrong, you're a true prophet, and if you get 50% or more wrong, and the rest right, then you're a false prophet. Or maybe you have to be 100% wrong all the time in order to be a false prophet. Or maybe you have to be wrong more than 70% of the time to be a false prophet. I would like to ask some of these people how much you can get wrong and still not be a false prophet. I suppose they could argue that you could get 99% wrong, and as long as you still got one genuine prophecy from God, you are a true prophet. They might respond to the above question by saying, "What is a true prophet if not somebody who gives true prophecies?"
Second, it's hard enough discovering that somebody is a true prophet and really hears from God. In all my life, I've never met such a person. But imagine if, on top of that difficulty, is the added difficulty of discovering whether any particular prophecy uttered by a true prophet is really from God! No matter how many times a prophet proved himself, you could never confidently listen to them.
Third, if a true prophet is sometimes mistaken, then they obviously can't distinguish between the voice of God and their own imagination. Why should they even trust their own prophecies if they know they can't make this distinction? If they are in no position to tell, think how much less the rest of us are in a position to tell!
Fourth, and finally, I've just never seen any Biblical justification for this position, while I have seen plenty of Biblical justification for calling somebody a "false prophet" who speaks presumptuously in the name of God.