I hope my merchant doesn't see this topic. I can guess his response, "It looks to difficult and risky, I'll stick with cash only".
I have a meeting with his later next week.
Well look, there is a risk everywhere. I think that the credit card chargeback rate is about 20-25% and merchants take this risk on themselves. But you are also using a logic that person that paid $3 for a cup of coffee won't be doing a chargeback. It's not worth a risk.
We can use the same logic about the Bitcoin double spend. But if you are looking for a 100% solution, I guess that Bitcoin is not ready for paying a coffee like Ciyam has said above. Honestly I am not sure that this will be ever necessary in order for Bitcoin to succeed.