If the player rolled low, they know that they’re probably not going to get anything useful, and wouldn’t trust anything you give them. But what if there were things you could tell the low-rolling player, other than something that’s obviously false?
Pick something from the following list, or roll randomly, as you see fit. And if you think of another option, use that one too. Shake things up a bit.
1. by accident, completely accurate
2. not relevant to question at hand; inaccurate
3. not relevant to question at hand; accurate
4. right emotion, but aimed at the wrong target
5. wrong emotion, but aimed at the right target
6. as far from the truth as possible while being plausible
7. hard to read; no information gained
8. good intentions towards the PCs
9. hostility towards the PCs
10. roll twice, and present both as possibilities
Notes:
1. Even a broken clock is right twice a day, after all.
2 and 3. For example, “You’re not sure if the warlord is lying when she says she’ll let you leave alive, but you’re pretty sure she desperately needs to go to the bathroom.”
4 and 5. If the priest is contemptuous of the scholar, these would give “The priest is contemptuous of the guard” or “The priest is afraid of the scholar.”
6. The key here is for it to be plausible; that’ll keep the players from rejecting it out of hand.
7. Use this if you don’t have the mental energy to come up with anything else, or if you need to move the game along quickly, or if the player just barely failed the Insight check and you don’t want to punish that.
8 and 9. These are regardless of whether it’s accurate or not. On a higher (but still not making the DC) roll, the player might not know whether they failed or succeeded, and this is the kind of information that could come from a successful Insight check.
10. If you enjoyed coming up with obviously false readings, here’s your chance to still indulge in those; give the player THREE options, of which two are plausible, and one is ridiculously fake. (”You think the prince has just had a nice meal so he’s in a good mood, or maybe he likes you guys, or maybe he’s an alien shapeshifter who hasn’t yet figured out how to work facial expressions other than ‘happy’.”)