After making a deal with Kevin, the idiot had him swear a couple of oaths on the name of Gods of businesses and dealers of truth, marking them as their witness that no one between them should break the rules, or they'll be punished by the aforementioned gods.
The oaths like these aren't just random promises and pinky swears, but something spoken and signed on the contract of honesty made through the churches of said gods.
Breaking these contracts meant sullying the name of that God and the church who issued these oath letters would know your sin and hold you responsible for blasphemous punishment.
As anyone can guess these things are extremely rare, and not something just anyone can take out at will, or order with money - how did Kevin get it, well no need to doubt since he's one lucky bastard, and found it on some roadside auction stall, or the dead body of some random bandit.
