Duration: Until commitment fulfilled (see below)
The wizard and the person they are making an agreement with, spit into their palms and shake hands to seal the agreement for a service to be rendered as the spell is cast.
Should the agreement be broken, for example by one party not providing the service in the agreed manner or period of time, a bright blue mark appears in the palm of the violator. This not only shows they have broken a commitment but allows them to be easily tracked by the spell Locate Spittle Bound and makes other divinations about the breacher easier as well.
Attempts to place impossible conditions on another through use of the spell cause it to fail.