It took me a few months to notice, but people here don't say no much. If you don't want to buy something, you say a sincere thank you, not no thank you. If you ask if there is mint today, you can assume that getting a long explanation means that there isn't any mint right now (even if you don't understand why there isn't any mint or when it will be available again).
I've finally managed to quit saying no thank you, but I still can't stop shaking my head when I say thank you (no matter how sincere). And I'm sure I'm too abrupt at other times too. But since part of the reason for never saying no is that everyone here is very polite, everyone is also too polite to tell me I'm not doing things the right way.