My party had secretly infiltrated a stronghold and we were Disguised (using magic) as the leadership of the place after eliminating the real leadership.
While rifling through the head honchos stuff we opened a chest that turned out to be alarmed and trapped. One of our party took some damage from the trap and the guards arrived soon thereafter.
Since we looked like members of the leadership, we went for a Bluff telling the guards it was a false alarm and that the injured character needed medical attention because he opened the chest before it was deactivated and before we could stop him ['That new guy, Bob, he just jumped the gun, whaddya gonna do with hired help these days?'].
Two of our characters did the talking and we each rolled Bluff -- poorly. Our basic message was a mix of truth and fiction (we accidentally set off the trap; one of is hurt and needs healing). The conversation with the guards continued and our GM had us roll Bluff again (I was secretly thankful since our first rolls were terrible). However, the other player didn't like this approach and got into a heated argument with the GM about how often we were rolling this skill check. This adventure does have us bluffing a lot and he doesn't like how often we roll in these interactions. The GM is fairly new and trying hard to stick to a script and felt that our characters were saying things in ways that were very different then who we were pretending to be. While I do think we are rolling a bit frequently, it's the GMs game and Rule 0 should apply.
Despite that, I thought I'd ask:
In a protracted conversation with NPCs where the players are lying, how often should they be rolling bluff? Every time they open their mouths, or less often ?