There are fairly low limits on the max transaction value with a debit card. You'd imagine that its simply down to what you have in your account but its not. Its also hard to get a clear answer (from AIB anyway) on what the limit is.

I would usually pay with a draft or EFT and make a second trip to collect, but last time, when buying the e60, I was tight for time so I used my credit card, but I used the same card to pay a holding deposit and told them I'd use the same card for payment. Having had the deposit paid successfully they were OK about accepting it for the balance. The dealer will usually want to charge a fee for this form of payment (I think ~1.5% is common) and you should let your credit card company know in advance that you may be making the payment so that it doesn't get knocked back on the day.

With the 5 I had done my homework, left Dublin early in the morning, confirmed all was as it seemed from the preparation and was leaving the dealer by about 10:00, back home in the mid-west by 7:00pm. Just to make sure I wasn't under pressure to buy a car that my head and heart mightn't have agreed on I had booked a return flight. That way I could make the right decision and the sales guy knew I didn't have to buy his car to get home.