What gets my goat is when a flight is advertised
$200 one-way
but when you try and book it it's return only.
Advertising standards should insist it read $400 return ONLY if it can't be obtained 1-way.
Best course: book a return, don't show up. It's usually cheaper than one way on standard carriers as opposed to LCCs.
I can't see why you couldn't book a one-way even at return cost - you'd at least save some taxes/charges...