Hmm, either this is a fake question, or you're really confused about a few things:
1) I'm not sure where you're from, but in America, most customer service tellers are required to say, "Have a nice day" and smile at you. Even if it's not required of them, they usually do it anyway because it's polite.
2) Just because someone says "Have a nice day" to you and smiles does NOT mean they like you, or have a crush on you, or have any sort of feelings for you. These are not the basis for thinking that.
3) If for some reason you think he really DOES like you, and is avoiding you, then next time you see him, you should try to initiate a conversation. If you've never talked to each other before, then you can start with something mundane (like the weather).
Anyway, I would further investigate your "relationship" to this guy before assuming anything. It would be awful if you got hurt because you assumed too much. :-)