Can you sell scrolls/units?
 

Or do I need to delete them

I read in one of those hints in between screens that you can sell scrolls in castles. Haven't tried it yet.

Don't know about units. Seems to me like you can't sell them.

You can sell scrolls and cannot sell units.

Only scrolls you can sale, not units . To sell scrolls while u are in a castle ( and only castle, does not work in inns, huts etc ) , open the spell book and right click the scroll to sale.