If it's so much based on D&D there is a lot of spells, talents, magic items or god's favors that allow you to fake your alignement and/or occupation from screening attempts of lower leveled characters...
And by the way Lawfull Good characters can also be awfully dangerous (burn the heretics, nobody expect the spanish inquition, etc...).
The strange tho, is that his wisdom is not a dump stat so he shouldn't be so guillible...