Pielorinho
Iron Fist of Pelor
Moderator's Notes: Keep the disagreement civil, please.
/Moderator
In fact (and I say this as a poster, not a mod), if you want to debate whether to use diplomacy or bluff rolls at all, you're probably better off starting a new thread on the subject, since the OP is pretty clearly asking what modifier to use, not whether to use one.
I agree with Takyris, that diplomacy could but doesn't figure into things as written. However, I'd give the player another chance: send the player an email saying, "I'll consider the bluff check, but if you want the diplomacy check to matter, you'll need to give me some diplomatizin'." I'd add, "You're aware that this is an extremely unlikely bluff: if your characters discovered some Draconians and goblins sneaking around your base, would you be likely to accept a similar explanation from them?"
That kind of feedback is, IMO, vital to helping characters understand the world in which they operate.
Also, and maybe this is just me being a big old softie, but I really like letting high dice rolls have at least some small benefit. Consider having a few of the goblins turn in confusion to one another, asking each other what the heck the "6th research party" is; if the PCs take quick advantage of the distraction, the combat will begin with a surprise round in which the distracted goblins may not act. This way, the player gets to enjoy having bluffed and rolled well, without letting a lame bluff completely break plausibility.
Daniel
/Moderator
In fact (and I say this as a poster, not a mod), if you want to debate whether to use diplomacy or bluff rolls at all, you're probably better off starting a new thread on the subject, since the OP is pretty clearly asking what modifier to use, not whether to use one.
I agree with Takyris, that diplomacy could but doesn't figure into things as written. However, I'd give the player another chance: send the player an email saying, "I'll consider the bluff check, but if you want the diplomacy check to matter, you'll need to give me some diplomatizin'." I'd add, "You're aware that this is an extremely unlikely bluff: if your characters discovered some Draconians and goblins sneaking around your base, would you be likely to accept a similar explanation from them?"
That kind of feedback is, IMO, vital to helping characters understand the world in which they operate.
Also, and maybe this is just me being a big old softie, but I really like letting high dice rolls have at least some small benefit. Consider having a few of the goblins turn in confusion to one another, asking each other what the heck the "6th research party" is; if the PCs take quick advantage of the distraction, the combat will begin with a surprise round in which the distracted goblins may not act. This way, the player gets to enjoy having bluffed and rolled well, without letting a lame bluff completely break plausibility.
Daniel