There is a competitor in the ad below me. He likes to increase his bid drastically - just to make me lose money big time! When he does that - he loses money also - but he makes me lose much more because my CTR is much higher than his and he knows that. So when he does that.. he loses X and I lose 10X or whatever.
Solution?
I encounter this all the time. An ad running in good position with a high bid and a much smaller CPC suddenly jumps in CPC. Someone just below me cranked up their bid. Depending on the situation, what I usually do is drop my bid until I'm just below him. My CPC drops to where it was, and it's not long before I have the position back.