We were having a diplomacy-off yesterday between the party and a higher level bard where we needed a succession of successes to beat the encounter. The issue was that it was basically a 50/50 shot for each diplomacy roll, as the best party member for us was equal to the NPC. Can Aid Another work for Diplomacy, as there was another character that has +10, and thus could always succeed at that? I'm assuming so.
I was also wondering if there are penalties for failing to Aid Another. I was looking in the pfsrd, but I didn't see anything like that under the skill section. We had two party members with no Diplomacy whatsoever, and so had a 50/50 shot of doing it successfully.
Edit: Not quite following the question in the title, but the Bardic Performance Inspire Competence can add +2 (at our level) to skill checks. Could this be used for diplomacy, or do individual diplomacy checks take much longer than rounds of performance can help?