Considering Flemeth offers you her book in exchange for her life, goes away and intends to possess Morrigan, yeah you do.
What Flemeth says is not necessarily the entire truth either. In DA:O, she's not entirely forthcoming, and even hints that Morrigan may be manipulating the Warden as well, which we later learn to be correct, since she withheld vital information until the time was right.
Morrigan isn't evil, though.
Flemeth is.
And yet Morrigan, for whatever reason, continues to carry out this plan to get one of the Wardens to provide her with the soul of the old god in infant form. At least in this case, Morrigan makes it clear that this was Flemeth's plan all along, but if Flemeth is evil for her scheming involving the Wardens, wouldn't that automatically make Morrigan so for carrying it out?
You can clearly see he possesses the warden that's present.
This does not preclude the possibility that Corypheus is actually dead, but in any case, Hawke does not have the player's savvy to notice the weird imagery or hear the creepy, foreboding music that hints that something is wrong.