How are bet results defined?

They are always defined from the premise of the bet. For example, if theres a bet that a team/player wins and then it loses or draws, the bet is considered lost: did the team/player win? No. So, the premise was not fulfilled.

On the other hand, the bet can be canceled when the result couldn't be defined by the moderators. There are multiple reasons why moderators might decide to cancel a bet. You will see them reflected in the notification that will arrive after moderation.