I would like your help in resolving a problem with a car rental. My wife and I rented an Opel Astra from Alamo on a recent visit to Ireland. When we arrived at the car rental counter, an agent told us the car we reserved was not available, but that she could get Budget to rent us a comparable car at the same rate.

When we received our credit card bill, we discovered that Budget had charged us $572 — more than 21/2 times the originally quoted rate of $222.

I admit that I signed the rental agreement with Budget, which in hindsight was a mistake. However, the Alamo representative led me to believe that Budget was charging me the Alamo quoted price. Had I known that we were paying more than twice what we were first quoted, I would have never agreed to the Budget rental.

I feel that Alamo owes us the difference between the first and second rate. I’ve been trying to resolve this with Alamo’s customer service department, with no luck. Can you help?

— Steve Chan, Camarillo, Calif.

Alamo did the right thing by offering to arrange a rental from another company when it ran out of Astras. But it should have covered all of your expenses, not just some of them.

This looks like it could have been a simple misunderstanding. Maybe Alamo gave the wrong rate information to Budget. Maybe Budget made an error in calculating your rate. It’s also possible that there was some currency confusion at work — substituting dollars for euros or euros for British pounds.

Car rental companies — actually, any travel company — will usually try to charge you the highest possible rate. (After all, they’re not running charities.) That’s why it’s so important to always be on guard, checking and double-checking every rate quote and bill before signing it.

Here’s what should have happened. When you checked in at the Alamo counter, you should have had a printout of your confirmed rate in hand. Alamo should have offered you two options. The company could have either upgraded you to the next class of car at no additional cost, or it could have paid for your entire rental through another company.

Assuming you still picked the second option, you needed to go to the Budget counter with the Alamo agent and verify that you were still getting the price you had agreed to. I know you realize now that simply signing the contract without reviewing it was a mistake, and I don’t want to make you feel any worse about it, but for future reference — always read before you sign!

Your signature makes it difficult to negotiate a refund from Alamo and all but impossible to pursue a credit card dispute or to take the company to court. Still, your situation wasn’t hopeless. If you reserved your car online, you might have argued that Alamo was breaking its best rate guarantee. Or, if you booked through a travel agent, you could have asked your travel adviser to help secure a refund.

I contacted Alamo on your behalf, and it issued a refund for the difference between the first and second rate.

Christopher Elliott is the ombudsman for National Geographic Traveler magazine. E-mail him at celliott@ngs.org, or troubleshoot your trip through his Web site, www.csr.elliott.org.