What I can't remember, is if it was related to trading, or if you can trade with Thisobald in the usual way at all.
I don't see how. In all my play-throughs, getting relatively close to him will automatically start the "Tav sits down at the bar"-sequence of events. Though perhaps this is different when you approach him from a different angle? I'll always take that ramp down from the first floor that leads directly to the bar/Thisobald. Plus I don't rightly know if the in-dialogue trade-button is clickable with him or not.
