Weird, why would she want to know about seducing creatures?
She can't think I.. Maybe she is one of those things?
Well lets play then. I raise my hand.
"How can we tell them apart?"

The cold voice starts to drone an answer.
"First thing you must do is narrow down your search group. Test your subject on attributes not shared by all the possible options. For example aply holy water, if the subject reacts in pain it is very likely to be an evil outsider like a demon or devil, or it may be undead. If nothing happens you can rule those out.

However remember that these rules are not set in stone, there are many variables and not all creatures of the same species always follow the same rules. A powerful vampire may have warded itself from divine power. And one fay is rarely like the other."

*bell rings*