As far as I can see, the only way to know what price you can sell a yes/no at is by having a long position already. If it is possible otherwise, it is not too obvious or helpful.
I think it is useful for people thinking about opening a position to have a sense of what price they could get if they had to immediately close that same position.
Would it be possible to display both the buy and sell offers on the offers tab of the market page?
This was actually a misunderstanding on my part. Nevermind.