Would you honor a handshake bet?

I'm not the betting type, mostly because it seems I always lose. But sometimes when I know I'm right about something I'll say "wanna bet?". Well, my friend took me up on it one day and we shook hands on the deal after betting a free dinner for the winner. I won and I told her to pay up but she's brushing it off like it's no big deal, like we were just joking. It's not that serious to me that I need the free dinner but it's the principle of the matter. If you shake hands with someone do you honor the deal?