I can vouch for that, I was commercial director of a well known charter airline back then and indeed on many flights the only profit was the duty free sales. We always worked on a target break even of 80% load factor ( charter remember so a fixed seat rate) but frequently on a 130 or 148 seat 737 the profit would be in the last five seats!
Back to my original post the irony is that I could now rebook the whole trip to connect to the earlier flight except as that is now offered by BA as a connection except I am sure they will not be able to do that either.
We will just go to the AC desk on landing in YVR and hope for no shows, problem being these flights are nearly always full and it is the week before Christmas which makes it even worse.
This is a trip we make often and in future will night stop at YVR then go over next day with either Harbour Air on the otter seaplane ( great little company) or just pick up the hire car in YVR and go by ferry. Might even do westjet over Calgary but AC have screwed me up one time too many now.