Please note that we've updated the Mount & Blade II: Bannerlord save file system which requires you to take certain steps in order for your save files to be compatible with e1.7.1 and any later updates. You can find the instructions here.
One of many, many examples where the item with worse modifier has the higher price. This doesn`t make much sense and is quite annoying when you want to keep the good stuff and have to look super careful to not sell the item with better modifiers.
Btw. the helmet with 18 head armor is the...