I've got 3 properties that are in an apparent flood zone. However they have never flooded, not in 2013, 2011, 1974, etc.... They are 1 in 100 year flood zones purely due to being within about 30m of a creek/stream that runs through the suburb. The stream never overflows. But they make a minimum flood zone around a stream regardless of whether or not it floods...
There isn't much impact on price. I saw one house in a the same zone sell for $450k instead of $480k which it would have gotten in a higher area. But that was because it was a subdividable block and you have to put a new house on posts off the ground so it obviously didn't appeal to as many people. My solution is to develop the land myself and put a qlder on it already off of the ground, so then there isn't an issue and you'd be getting normal price for the sale.
However if a house was in a very frequent flood zone and it wasn't easy to raise the place above the flood height, I would probably give it a miss unless it was ridiculously cheap.