This would actually be a Bluff check, but as the roll is high enough, it would still apply.
The scarred man looks Lavinia up and down, as if trying to determine the voracity of the eladrin lady's statement. Coming to a seeming conclusion, the man smiles at you.
"Hmm...you sound sincere...be careful about telling too many truths in the City of Lies. Perhaps this is why he may take over your business. Although, getting involved in the Mark of Shadow's business could be very dangerous, we'll just add it to the bill later...You must be desperate coming to me. Meet me at midnight tonight, and we will discuss these arrangements."The shadows envelope around him, and when the light returns to the area, he is gone.
However, he is not quite quick enough to totally escape notice. Vennerzad can see him briefly come out of the shadows, pull up a rug on the floor, and exit through a hidden trapdoor. It seems you may have discovered their hideout!