On the standing page, there is a "conference information" link for each division. The conference information page displays a box for 8 teams, and in that box, it will tell you when the manager was last seen. If the box is blank where there is normally "last seen" information, then that team is a bot.
Alternatively, if you go to a team's page, and it says that the Manager is "Managed by a computerized player", then that team is a bot.