Today, I booked a United itinerary in Economy from Canada (Halifax, NS - YHZ) to the US and back over the phone. (The flights I wanted would not show up on the United website.)

The agent informed me that there was a "non-ticketable tax" of CAD 10 which I would have to pay before departure at the airport.

I've flown numerous times from Canada to the US, and I never had to pay any tax at the airport. So I asked, and she repeated that I would have to pay CAD 10 at the airport. And it is not a baggage fee.

Still, I do not believe the agent. But why would she say that?