I will be sure to read it thoroughly before ordering.
I agree that if you state in your TOS that prices are set in USD and refunds will be given based on that then you are being fair.
Think this sentence makes it clear?
If we have to refund, we will do so according to the value of the item in USD or EUR at the time.
Longer version:
In the case that we have to refund you, we will refund you in a currency of your choice (USD, EUR, BTC) according to the value of the item in USD or EUR at the time the order was placed.
Yikes. Is that really the business practice you want to engage in?
What if you don't even send the product, as is the case of this thread? You're going to "refund" (i.e. give the person his money back -- the money that was never yours to begin with) in a different currency because you want to keep some of it?