I've yet to see anyone with a policy that formally "allows" refunds on virtual currency.
That being said, you should treat each complaint individually. Is it that big of a deal to refund that money? Did they spend any of it before asking for a refund?
Personally, I think a "no refunds" policy is a great idea. That being said, I seriously doubt you should allow single purchases of over $100 at any time. I suggest you don't even provide currency packages of over $20 to start with, simply because buyer's remorse will increase with the newness of the games/company, thus incraesing the chance they may want to back out of their purchase.