I think it's reasonable to inflate prices 12%
I do not.
it takes courage for us merchants to accept bitcoins.
Yes. The time it takes to exchange could work in your favor as well.
If you're gambling you're not running a business. Business is about profit. Right now, paying a premium on BTC-related purchases is understandable. You should expect to pay 10% extra, not 10% less. That can change when you have 1.) a competitive economy and 2.) stability in volatility. The name of the business game for now is fiat, not BTC.