If you rent a car in Ireland, confirm by email the total charge you will incur BEFORE you fly there.
We rented a car for our trip to Ireland from Europcar. The amount shown online was 103.32 Euros. The billed amount was $486, or about 374 Euros.
When I emailed Europcar, their response was, "You signed the contract at the desk when you rented the car, so you're liable for the amount on the contract you signed".
When I mentioned the term "consumer fraud" in my next email and told them I had saved a copy of the online contract, and that as far as I was concerned, I signed the contract in the US, so US law applied, Europcar cut $100 from my bill but did not email me again. I found out about the partial refund when I called my my credit card company to dispute the charge.