I am having the same problem but only with some goods, Batavian Spices, Port royal price in shop 300 paid 150, luckily I have been court earlier today selling gold and checked by just selling one. some goods such a iron sold as per price. so its is not just strait forward, 30 min later Batavian spice sold at the listed price of 300 totally inconsistant
You need to sell one and if it match the current price sell others. basically stop me trading in store and because it is so inconstant you simply can't tell when it will happen this need fixing not just waiting till next up date with more bugs. love the game but the last patch while it introduced some good changes made the game more buggy and inconsistent. not heard more than one positive comment since last update,