Rental cars are tight under any circumstances in Ireland. Having a firm reservation, a definite pick up time and a Hertz #1 Club Gold membership didn't even help me on one of my recent trips to Dublin. The Hertz agency in Donnybrook was out of vehicles and wasn't able to fulfill my rez with anything. I took a taxi back to the Westbury and, with the help of the concierge, was able to rent a late model Spec from Avis.