We have a customer who is disputing a charge done in Brussels. They claim when the bill was paid, it was twice the amount they ordered. After taking it up with the manager, they went ahead and paid the bill to avoid a scene in a foreign country.

In my opinion, this implies they authorized the charge, and have no chargeback rights.

Any thoughts?

I agree. Any chargeback that you file will result in the bank receiving a receipt that they signed. This dispute is solely between the cardholder and the merchant. Deny the claim and move on to the next one.