how does shopping with store credit work?

[Rolig Loon]

It all depends on the store.  There is no "standard" model.  Each merchant who decides to do something like this invents her own set of rules and then usually uses one of several commercial scripts to make the gift cards work.  A gift card usually comes with some sort of instructions about how to use it, and there are usually instructions somewhere in the in-world shop too.  There may also be instructions in a dialog menu when you go to buy something in the shop.

[Rolig Loon]

It all depends on the store.  There is no "standard" model.  Each merchant who decides to do something like this invents her own set of rules and then usually uses one of several commercial scripts to make the gift cards work.  A gift card usually comes with some sort of instructions about how to use it, and there are usually instructions somewhere in the in-world shop too.  There may also be instructions in a dialog menu when you go to buy something in the shop.