I set daily limit 50$. I put higher bid by mistake ($15 instead $0.15). After few hours I see 57 clicks - cost $225!!!!! I see on AdWords help that they can overcharge me by 20% per day. But it is 450%. BTW, I have no this money in my adwords account. I have only $100 in my Adwords (prepaid account). How Adwords can deliver this amount of clicks (higher than account ballance and daily limit overcharge 450%).
I had same problem two days ago. I put maximum limit for spepending in one campaign and it did not work. But that campaign was in shared budget plan so i must pause it to stop overspending.