You are skilled at negotiating with outsiders for their services.
In addition, you receive a +4 bonus on any checks associated with such bargains or to attempts to compel service (such as with planar binding). This bonus also applies when testing the trap of a planar binding against the outsider’s spell resistance.
If you succeed in this check, the contract you form with the outsider is worded in such a way to prevent the outsider from taking intentional actions that are harmful to you and your cause (subject to the GMs interpretation.)
Way of the Wicked Book Five — The Devil My Only Master. Copyright 2012, Fire Mountain Games LLC; Author: Gary McBride.