It's my first time GM-ing, and one of my players has a PC with a background she wants kept hidden. Whenever her character lies, i secretly roll a bluff check for her, and a sense motive check for whoever is listening, including NPCs.
one NPC succeeded and confronted her about her story away from the rest of the party, and proceeds to interrogate her about the truth. she went ahead and told a new lie, "you're right, i'm actually here for such and such". the NPC goes on to ask questions about the new story.
so my question is, as the story gets more elaborate and detailed (specific names etc.), how many times should i roll a bluff check? it seems to me that if you keep making stuff up, it shouldn't be just one check for a entire conversation, one side of which is total falsehood.
where do you draw the line? a check for each incorrect fact? per period of time lying? for the entire conversation? every time the PC has to make something up on the spot?
appreciate any thought or experience in this matter... thanks!