A WebmasterWorld thread uncovers a bit of the details behind the frustration an international advertiser may have when being charged for clicks by Google. AdWords advertisers, like the one in the thread, pays Google is his local currency. Google needs to use an exchange rate to convert that currency into US currency. Google, however, does not release the source of the exchange rate used for the conversion.
The official response from Google about the exchange rate is that "Google is unable to inform you of how the exchange rate is calculated."
AdWordsAdvisor2 is on record as making a case for Google to release the exchange rate source to the advertisers. We will see if this happens. But it is clear to me that the advertiser has a right to know this information. Especially when he feels that the rate is "horrible."
Forum discussion at WebmasterWorld .