At this point, I'm done wasting time on this issue. I'm out $48.83 and it's no longer worth my effort to keep pursuing.

I figured I would share my experience so others know what to expect.

The Situation:
Booked an Avis Rental via Chase Travel Center prepaid with UR points and cash. Itinerary clearly states "The total price includes all mandatory taxes and fees."

Pickup/Drop-off Location is clearly indicated on Itinerary. Panama City (Tocumen International).

Avis refused to give me the rental until I paid an additional $48.83 for a 'mandatory airport fee'. After arguing with the agent and unable to get through to the Chase Travel Center, I put the charge on my Sapphire Reserve as it is very late and I have the whole family with me. After getting back to the states, I disputed the $48.83 with Chase.

Despite two rounds of submitting my documentation and talking to several 'agents', it is very clear that Chase understands the situation and does not intend to make it right. Chase Travel Center reps verbally repeat that the itinerary includes all mandatory taxes and fees, but will not send me a breakdown of what they paid in writing. Chase Sapphire reps repeatedly want to 'mediate' a call with Avis to kindly ask for refund from them (interesting how long the agent was willing to wait on hold with me to call Avis), but each time I run out of time before getting through to an Avis Rep. Chase Sapphire Rep and Chase Travel Center reps refuse to reach out to each other.

My situation involved a car rental, but via Google searches did find at least one person complain about the same thing happening with a Hotel Reservation (Didn't see any followup if they disputed with Chase).

Personally, I don't have any advice on what else to do if this happens to you, but know that it won't be as simple as disputing the charge later if you do decide to pay the surprise charges.

This is one data point and is likely to be uncommon as I don't see anyone else complaining about it in the Flyertalk Forums.