For nearly a month now, I've been fighting to recover more than $280 from Hertz in connection with a reservation for a Mexican rental I made through Hotwire.

I reserved a Hertz car for a week in Mexico for an estimated $113 - a flat $90 for the rental of the car, and an estimated $23 in taxes and fees. I did not pay Hotwire at the time of the reservation and understood that I would pay Hertz directly when I rented the car.

At the Hertz desk in Mexico, I was presented with an entirely different set of charges. There, I heard for the first time about the mandatory Mexican liability insurance. I did not have the option of declining the insurance, which amounted to approximately $110 for the week.

But that wasn't the only surprising charge. The price of the car had mysteriously risen to about $108, and I was assessed a "service charge" of approximately $135. No one at Hertz or Hotwire has yet been able to tell me what that's about. Together with two smaller fees of about $44, my total bill came to $397.

The day after I returned from Mexico, I contacted both Hotwire and Hertz. Although their stories have varied slightly over the weeks, each company tells me that I should go talk to the other. Hotwire says it has no control over what Hertz bills me, and Hertz says it has no control over what Hotwire quotes me.

Given the enormous discrepancy in price and the hours I've spent trying to get this matter resolved, I am seeking a refund of the difference between the $113 reservation price and $397 charge. Hertz has my money, but Hotwire made the representations that led me to the Hertz desk in Mexico. Can you help me get my refund?

- B.P-D., Arlington, Va.
Answer: You should have been charged the rate you were quoted. When you weren't, Hotwire should have asked Hertz to refund the money on your behalf.

I checked with both Hotwire and Hertz, but could find nothing that specifically addresses your situation. (Hertz has a lengthy page with disclaimers about its protection plans that came the closest:

Did someone in Mexico pull a fast one on your rental? Possibly. After you returned, a Hertz representative in the States told you that insurance wasn't required on your rental. If a Hertz employee in Mexico told you otherwise - and insisted you buy insurance before allowing you to leave - then you can be forgiven for thinking your car rental company was trying to separate you from your pesos.

One of the best ways of preventing an insurance misunderstanding is to do a little homework before your trip. Contact your car rental company and get your insurance requirements in writing. Make a printout of your credit-card coverage and car insurance coverage, too.

When an agent demands that you buy "optional" insurance, take a step back from the counter and call the car rental company's reservations line. Explain the situation, and ask for a resolution. It is in the car rental company's best interests to fix the problem right then and there, and I've seen companies rise to the occasion time and again when called.

If you've already taken the insurance, stay off the phone. Instead, contact your travel agent or car rental company by e-mail. Having a paper trail (or in this case, a data trail) ensures your grievance will be addressed quickly and taken as seriously as possible.

I contacted Hotwire on your behalf. A Hertz representative contacted you and agreed to credit you the difference between the amount charged to your credit card and the amount quoted to you by Hotwire.