New DMC store - not substracting money. How to?

Hi and hello, I'm new here.
I'm trying to create a mod which adds a store to DMC. I have successfully added location, encounters chain and treasure table with items. One thing is not working: when I pick up item the money amount is not substracted from player. Can't find a solution.

Q1: Is it possible to create a store or are stores hardcoded into a game?

Q2: How can I make store sell items for price?

Thanks