It's pretty much how the merchants that accept bitcoin are handling it right now. It's flying fine.

No, it's one of the things you have to consider before accepting Bitcoin. Overstock for example gives store credit and is explicitly says up front that is what they are doing. Anyone that tries to refund in USD at the current exchange rate instead of returning the original payment w/o stating upfront that is what they are going to do is being hugely dishonest. Think about it what if you tried to return your laptop to Sony and they said find but we are going to refund your money in JPY instead of USD and o by the way the exchange rate has changed 10% since you bought this so here is a refund for 10% less. No way that would fly so I'm surprised people would think doing the same with Bitcoin would be ok.

I believe the larger merchants (e.g., Overstock) may not even be giving refunds right now. When buying with Bitcoin you can only get store credit.