One of the things i always liked in this novel was the 30% discount. It isnt even strange that no merchant doubts the price they give. The calculation skill will have been tested and tested and tested, to the point that someone adding up actually counting and getting a different price would be seen as making a mistake. The skill is something every single person with a merchant job has and it has never given a wrong answer. Why bother to learn to calculate when this skill will do it all and never fail?
Oh and best girl is finally here. Roxanne always annoyed me in the novel though i do like her more in the manga, but Sherry will always be my fav and she looks amazing in this too.