wpForo has a simple yet powerful user reputation system. It’s under active improvement, currently it based on number of posts.
There are ten levels of User Ranks. Each level has its Reputation Title and Badge. You can manage level posts, titles, badges in Members Settings admin page (Dashboard > Forum > Settings > Members)
Set Custom Reputation to a User
In case you want to change some user reputation, you can use according option in Dashboard > Edit User admin page.
By default all members get rating badges and titles based on number of posts. However, using this option you can grant lower or higher rating to certain user (this user). The default member reputation badges, titles and points can be managed in Forums > Settings > Members Tab.