This is a good move to target Bitcoin holders.

However I have a concern, how do you handle the risk of refunding Bitcoin in USD? The BTC/USD rate will surely move from the date of sale to date of refund.

Example
Date of sale 15 Oct 2017: 1 BTC = USD  6000
Date of refund 25 Oct 2017: 1 BTC = USD 6500

In the above example, you receive 1 BTC for a USD 6000 sale. But you are refunding USD 6500 for 1 BTC. On the other hand, if BTC weaken against USD, the customer will be suffering losses of USD 500.