Soon also may not have bothered to check.
A ruse that relies on the target's innate acceptance of the rules presented to him? Against a league of paladins? Easy money.
It occurs to me that even if Soon had discovered he was deceived at some point, he'd still sworn an oath not to contact Girard again for any reason, even to get the right coords. Not sure how Hinjo would avoid hearing about it if Soon knew, though.