This came up in a game the other day, where the players were trying to convince a mob boss who ran a casino that the PC's weren't cheating when they won a landspeeder. Technically one of the PCs felt destiny guide them to the slot machine due to the force, but the player didn't even *know* that.
I realized that none of the skills really fit what they were trying to do, and there is a lack of the usual 'convince' talents that normally come with an RPG.
For example, it wasn't a negotiation - they weren't trying to barter or trade anything, and it wasn't coercion as they weren't trying to intimidate him. It wasn't deception since they were telling the truth. It wasn't even charm, as they weren't trying to be charming or give puppy dog eyes.
So what would you have told them to roll? I told them they could pick charm or negotiate, whichever was higher, but it definitely didn't feel right.