Unethical for sure: they know there is a recurring problem with debit/credit cards and only leave it in the T&C - realising full-well that the deals aren't half as good if they would be clearer about the issue. In the end, they wanted to charge me double what the booking first cost at the counter (ie telling the first!) - and the same happened to others in line - in my country, Hungary, credit cards are not the norm, everyone uses debit cards. I refused to pay, rented a car at another company (Avis - for some reason they were fine with my debit card) and it cost about the same as the surcharge i would have had to pay for my Rentalcars.com booking. I contacted them, they knew the issue before I spelled it out and refused to refund... Sounds like a scam to me.