The Charges can only be refunded back when the Return Order or RMA is generated and needs to have an item associated to the return for it to be processed, even if it is a header charge.
because they should have been tax exempt but got charged
It looks like the taxes are applied dynamically and do not track if they have been refunded or not.
ability to adjust sales price, Price Match functionality
Need to honor promotional pricing if it happens within a specific time frame or competitor prices.
Since this information is tracked at the item level on what the new price is, I would assume that the Return Order would pull that information in and not the information on the Salesline.
All these scenarios, while I can refund back money to the customer through the ORDER CREDIT feature, it does not track what was already refunded and if the customer tries to refund them their order it will refund the total amount of the original order since no knowledge of the Order Credits can be identified. I would also like to know if the Order Credit feature can have the option to apply the default call center refund method so that it does not create an Credit on the customer account, which requires AR to run the customer balances and refund any overages, but generate the refund check like the return order process does.