The Perfumed Seneschal - Revisited
The Perfumed Seneschal has been at large these sixteen years. I only started theory crafting last year, so I thought I'd give this one a try.
Quaithe is a glass candle user and we're told of their capabilities. Seeing long distances, projecting yourself into a person's dreams and causing visions. But prophecy is not among their uses. For everything else that they do, glass candles do not give visions of the future in the sense that the nightfires or weirwoods do.
So nothing prevents her from saying "Quentyn Martell" is coming and you shouldn't trust him. But by using sigils and codes instead, she leaves room for uncertainty. Daenerys would remember if "Aegon Targaryen" never showed, but the "mummer's dragon" could slip her mind.
In this way, she can cover for the fact that Jon and Aegon decide to go west at the last moment. Because things can change quickly; Quaithe is giving dispatches, not prophecies. The conclusion I take from this is that perfumed seneschal is encoded, just like "sun's son" or "mummer's dragon" ie. we're not looking for a literal perfume-wearing seneschal.
The last part of this re-examination is "beware." Knowing that Quaithe has at best, access to the recent past, she would not be able to expressly tell her to beware a far future threat. Like Beware of Dog, or Beware of Deep Water, Quaithe is warning of a threat that is right in the here and now. A threat that she hasn't noticed.
So, I'd say we're looking for someone, who isn't a literal perfumed seneschal (that would be Reznak mo Reznak) but someone who could be described that way.
Perfume covers up unpleasant things (Ilyrio), or serves as part of a costume (Varys) and that's the sense we should think of the Perfumed Seneschal. Someone who is hiding their true nature under a sweet exterior.
Beware the person who serves you who isn't what they seem; that's the Perfumed Seneschal.