I know there’s not a hard answer to this so I’m putting it in IMHO. In modern times in western society we often tend to assume all fortune tellers are more or less just con artists, or at best entertainers, of one kind or another.
Does any historical research reveal whether ancient oracles took themselves, and their jobs seriously, or was it all just a big con game to them as well?
In the extras in the 300 DVD, historian Bettany Hughes said that they used to burn some kind of hallucinogenic plant and inhale the fumes and then babble out all kinds of disconnected stuff, which was thought to be the gods speaking through her body, and you or the priests would then try to interpret what she was saying.
So it seems they were more or less sincere, I guess, although personally I wouldn’t rule out the con artist thing either.
Cicero’s treatise De Divinatione (“concering Divination”) gives details of the various divination methods used by the Romans. In it he discusses the role of the haruspex, who interpreted the divine will by inspecting the entrails of sacrificed animals. Cicero comments:
suggesting, possibly, that some of the haruspices didn’t take their role very seriously.
I imagine they ran the gamut.
Anecdote- I have a friend who genuinely believes she can foretell the future. For a brief time, she worked for a dial a psychic 900 number. She quit because she felt ‘The company was much more interested in money than in helping people’.