I would call Carmel and have them credit that $8 back to you and I'd have them reduce whatever automatic tip they charged. It states on their own website that "not every trip to/from an airport incures tolls". You are never charged a toll unless one is charged. That is standard with every car service. Carmel is a very large dispatch service and your driver would have had no problem picking up a fare at EWR. The only time I've seen a "come back toll" charged is on a specialty car, like a limousine, where they may not have a fare booked back.