@Kikaibaka not trustworthy no, especially not to their enemies (like you said, someone who stole a gods book is likely to be targeted by rival gods clerics as they think he belongs to that "evil god"). But they are also not evil underhanded people, so drawing that "smile smile, im a villain" face is pretty stupid.
edit: or if they are unaware that the book he stole was from the evil god, they might just think he is someone who disrespected a deity and stole from her, making it apt to dispense some justice.