WTF? Scenario:
- Buyer pays you 100 BTC for something.
- BTC's worth doubles in USD.
- You don't send what Buyer ordered.
- Buyer (obviously) wants a refund.
- You'd then try to only owe Buyer 50 BTC?
The only one getting screwed would be the Buyer. Comparative value is meaningless. The Buyer cares about what he paid in his/her bitcoin. Alternatively, if bitcoin became half as much in USD, Buyer would still be owed 100 BTC. How is it possible to not see how unfair it is to be refunded in anything other than the original amount?
Suppose, the Gold coin was sent. The buyer still gets screwed (because his good is only worth 50 when he paid 100) by that logic.
In your way, the buyer takes the risk and the seller may manipulate the refund for their own profit. If the value rises then give the goods. If the value falls then "oops, we were actually out of stock" and give a refund. (I know it didn't happen in this case, but I have no doubt that it has happened)
In my way the seller takes the risk and buyer doesn't' care if the refund happens. Independent of the value of Bitcoins and whether the refund occurs, the Buyer still has the same buying power and may buy the same product elsewhere. Independent of a corrupt seller, the buyer can end up with what they wanted by loosing no extra money!
(And people think about the value of their Bitcoins anytime they make a purchase, not the number. If that wasn't the case then no one would have bought a pizza for 10,000.)
I actually can't see how your method is fair and mine is unfair. I would say that refunding only 100 if the value dropped was unfair. I would certainly feel cheated and suspect foul play.