The voice overs and overhead text probably follow one another in the script with a timer afterwards (at least that's how I'd script it). I looked through the main campaign script editor yesterday and couldn't find such a script for the cheese vendor though. He just had a normal start dialog one. I'm not certain where Larian scripted the overhead text or VOs.
Having a bunch of salesmen shouting things in the marketplace set the atmosphere for me but what I didn't like was my chat bar getting flooded with repeat text. BioWare did similar overhead VO text with the Baldur's Gate series but I don't recall it ever getting in the way. Larian may tweak it eventually but it's probably low on their to do list as there's other more serious issues they need to fix first, as well as updating the editor to make it easier to use.
