Invoice/Inventory/Credit confusion

[Charley Tiggs <..hidden..>]

I think I've confused myself with regards to how to handle inventory in 
the event of a customer wanting to exchange an item.  Here's the scenario:

Customer buys product, is invoiced, inventory is reduced.

Customer receives product and realizes it's the wrong thing for various 
reasons.

Customer returns product and wants to exchange it for the right item.

This is where I get confused:

Item is accepted for return, an invoice is created and qty is marked as 
negative so that item is returned to inventory.  When I go to the 
Cash->Receipts screen for that order, the invoice shows up as something 
that needs to be paid with a negative dollar amount.  So, what'd I do 
wrong?  The customer should have a credit against the original invoice 
and all I want to do is make sure that user has "store credit" that they 
can then apply to the item they have requested in exchange.

Is there a better way to do this or have I missed a few steps?

Charley