Ferry companies do this .......
I know of cases where an airline has done the same, and that others plan to follow suit particularly in cases of repeated 'abuse' by the same passenger. In one case, where the tickets were purchased through a travel agency, the agency received an ADM (agency debit memo) from the airline, for the difference between the 'cheap' reutrn and the full oneway fare, passing the onus of collection to them, which in my view is grossly unfair.
I think this
stinks but such is the reality of the world we live in.