yeah, it happens a bit. but most of the really great gear requires you to fight a pretty tough opponent or party, in bgII. money is spent mostly on recharging wands and buying potions, there really isnt so much good gear on the shelves. you may want to buy baldurans armour or the belt of strength, but to raise such large sums you must fight through several encounters that usually give you better stuff anyway.
rest assured that if you want the best sword / stave / ring, they cant be bought: you will have to fight many beast obscura.