Europcar should have furnished your credit card company with the documents necessary to process your claim. If your accident had happened in the States, the car rental company probably would have sent you a damage claim instead of charging you immediately, but “charge first, ask questions later” seems to be the way things are handled in Europe.
When a car rental company bills you $3,309, it is obligated to show that it actually paid that much to repair your vehicle. You didn’t contest the charge, but Europcar needed to work with you to process your claim with Capital One.
I don’t think your credit card company has a double standard. It doesn’t determine if a charge is right, so it couldn’t have known whether the initial damage claim was legitimate. A separate department handles the insurance claims, and knowing big bureaucracies as well as I do, I think it’s unlikely that Capital One could have done the math and determined that the Europcar charge wasn’t legit.
Some might contend that your case is a good argument for buying a car rental company’s insurance. I disagree. You were fully covered under your Capital One policy. The CDW offered by Europcar would have been an expensive and unnecessary cost.
I might have pressed this issue with Europcar in writing. Email addresses for its employees follow the convention: firstname.lastname@example.org, and a little Internet sleuthing would have turned up the name of a manager or supervisor. The company needed to furnish you with the documents; it can’t just charge you based on an estimate.
I contacted Europcar on your behalf. A representative emailed you the damage appraisal receipts, which allowed you to make a successful claim with your credit card company.