They didn't play fair though with the that woman (forgot her name) who was held hostage then released then later ended up dead in this episode, when she talked to the police it made it sound like she heard two people talking to each other.
I can think of two reasons for this.
I really don't get the Gellar thing. If it was meant to be a twist that he was really dead then why make it so blindly obvious. Why constantly refer to Gellar as Travis' Dark Passenger. It almost seems like they changed their mind and originally wanted us to think he was dead and then decided fuck it lets just have him being dead.
Awful writing. Awful.
One: the writers didn't think it would be that obvious. Maybe they hadn't counted on people having seen this twist so many times before, at least since The Sixth Sense came out. And, tbh, if that film came out today, a lot more people would be guessing the twist. It's a cliche now, and maybe the writers didn't realise that.
Two: they made it obvious on purpose, using it as a smokescreen for a bigger twist to come in the next couple of episodes.
I hope it's the second one. It's unlikely, though. I guess I just can't believe that the writers thought nobody would notice Geller's invisibility to everyone except Travis.