Accounting for store credit purchases

[ShannonClark]

Hey guys,

How does the Shopify system account for purchases made with store credit? 

Basically when customers return a product I want to offer a refund with a fee (restock fee) OR store credit (no fee) that expires in one week (they will be made aware of that). 

But I’d prefer for their new purchase not to be reflected in total sales because I didn’t have more money come in for it (basically the old sale now becomes this sale).

I do not want to refund them money however because then I suffer the processing fee.

Is there a way to do this?