Angels cannot tell lies and will only tell the truth or avoid speaking altogether if they cannot be truthful. Whether this is due to their obligations to God or they are simply incapable of conceiving of lying is unknown. Angels will verify their identity and stick to the point of their visit to you. They will stay on topic and quickly depart once their message is delivered or their mission carried out for they detest being away from their Lord for long.
Demons, by contrast, are habitual liars that disguise themselves as angels to lure the innocent and ignorant. They too, will claim to be an angel but will attempt to engage in conversation with you. Never speak to a demon, no matter how innocent or well-meaning their inquiries may be as they can and will use any information they glean against you.
—St. Ignacio Navarra, Treatise on the Celestial and the Demonic. circa.1656