I booked a rental thru Auto Europe UK for about 40% less than the US site. I did call the US customer service, who verified that it was fine for a US person to do that. When I was speaking with a rep from their affiliated company Kemwel, she warned me that it was possible that the rental agency might refuse to honor the reservation when they saw that I had a US drivers license instead of a UK license. Has anyone had this problem and been refused or forced to pay more?
I just rented 2 minivans in Germany from www.autoeurope.eu which had greatly discounted rates over www.autoeurope.com When I picked up my car they didn't mention anything at all about my USA drivers license. I wouldn't worry about it.