Q: I rented a car from Thrifty in Los Angeles. The car I had reserved was not available when I arrived, which I only learned after waiting over an hour in line! Thankfully, a kind agent found an available car for me. Unfortunately, it looks like Thrifty also increased the price of my rental by $250.

Each time I ask about the charge, I get a different response. When I signed the rental contract, the agent advised me to contact Thrifty's main office during my rental to correct the overcharge. When I contacted Thrifty during my rental, they told me to wait until after the contract was complete. Now I'm being told that I should have ensured that this issue was addressed at the time of signing the contract.

I never asked for an upgrade. I've written to Thrifty and have asked for a refund, but it refuses. Can you help me?

A: Thrifty shouldn't have made you wait more than an hour, and it shouldn't have charged you an extra $250 without your consent. The industry's standard practice when a location runs out of cars is to upgrade a customer to the next available class at no additional charge.

The kind agent should have been clearer about the additional expense of an upgrade or urged you to wait until the Thrifty location had a car in your class (which might have been a longer wait).

I've been seeing a lot of these car rental shenanigans. The location runs out of cars, and then a "helpful" agent slides a contract under your nose that includes a hefty upgrade charge. If an agent ever tells you to call the 800 number to correct the overcharge, walk away. The moment you accept the keys, you're on the hook for the full amount, no matter what an employee says.

Even if you've already agreed to the rental, you still have a decent case. Make sure that you keep the original reservation; then send a copy of the confirmation, along with the new invoice, to the company and politely ask it to adjust your rate.

But Thrifty's responses were predictable, stating that you signed the contract, so you have to pay. There were "sincere" apologies for the way you felt about your rental, but Thrifty would not budge.

That's troubling. You trusted the Thrifty agent to do the right thing, and instead, the company stuck you with a $250 bill. Maybe you're renting from the wrong company.

You told me you were so exasperated that you felt like dropping the matter. But I had a better idea — I contacted Thrifty on your behalf. The company refunded your $250.

Christopher Elliott is the founder of the nonprofit Elliott Advocacy. Contact him at chris@elliott.org or elliottadvocacy.org/help.