I miss understood the question. Before booking the ticket, there is just educated guesswork. I would agree that that looks like AC language for the rules. But who can say?
I'd be reluctant to book with anyone who can't tell you up front what you are actually buying. It doesn't seem worth saving ... really any amount of money. Its either a trivial amount, or it is for sure too good to be true.
Wait for a seat sale, sure, but the safe and reliable ac.com or the guys in the mall for 20 years is the way to go. The $20 is not worth it.