the most important ones
the main castle
the shop next to your main castle
then to mage tower(point where u get the rage box)
and possibly the 3 castles there(sometimes i am too lazy to check there)
and at graveyard the furious paladin
rest of the shops aren't that important
but nonetheless there is always a chance there is a good item hidden in there
it never hurts to scout all shops on darion(if your sure you want a good item start)
you save at start of the adventure anyway
and after your done scouting all shops and noted the good items or not
reload from save or start over again and redo ^^