As for the condition of the bow, if someone like Big Jim says it shouldn't be a problem, I personally wouldn't be too concerned about it (the super glue option would give you more peace of mind).
As far as getting some kind of compensation from the buyer... at the end of the day, it never hurts to bring it up. There is a chance the seller was unaware of the crack and wasn't trying to be deceitful. But, if they don't want to deal with you, unless you had some kind of trial arrangement where you could thoroughly look it over before committing to the sale price, then you're left with send it back or keep it.