There is the WRONG belief that everyone is your “brother” and you are supposed to let your guard down.
Good point LongHairGal, especially in consideration of Barbara's comments about how pedophiles often take the most interest when JW's do prison ministry. If we don't have a prison located near to us, we might not give much thought to prison ministry but people, including JW's, do tend to move around. How much more so for someone recently released, trying to escape their past and starting a new life as a JW?
Any new JW that suddenly shows-up at the hall is expected to be welcomed with open arms and full trust, even as no one (except a few elders - may be) may know anything about the person.