Eventually he needs to learn about a lot of stuff, sales tactics or the items' abilities for example, but I don't think that's gonna happen if the girls do everything for him.
Ah no.. This manga is a "how to run/work in a <em>japanese</em> shop" tutorial for kids..
With all the Overhead in culture and manners that comes with that, the MC must make all the Basic Mistakes, while being "funny".
So... Dense when it comes to romance, dense when it comes to business, dense when it comes to people skills.
It's easy to peg this one for what it is...