The line between skills isn't that clean.
Especially when you're just free-formin' it and doing some Overcomes for the sake of plot, not really in a C, just hangin'. So let's look at what you can Overcome with Deceive and Rapport, maybe get some ideas. SRD, take me away!
Use Deceive to bluff your way past someone, or to get someone to believe a lie, or to get something out of someone because they believe in one of your lies. For nameless NPCs, this is just an overcome roll, but for PCs or named NPCs, it requires a contest, and the target opposes with Empathy. Winning this contest could justify placing a situation aspect on your target, if buying into your lie could help you in a future scene. You can also use Deceive to do small tricks of sleight-of-hand and misdirection.
-- Deceive, from the Fate SRD
Use Rapport to charm or inspire people to do what you want, or to establish a good connection with them. Charm your way past the guard, convince someone to take you into their confidence, or become the man of the hour at the local tavern. For nameless NPCs, this is just an overcome action, but you may have to enter a contest to sufficiently ingratiate yourself to a named NPC or PC.
-- Rapport, from the Fate SRD
Is there a bright clear line between "bluff your way past" and "charm your way past"? Nnnnnot necessarily. If a guard knows you're not supposed to be somewhere, then getting there is going to involve some kind of... "creative truthtelling", at least. It's going to lean more toward presenting falsehoods and getting the guard to believe in them for Deceive, and more toward making it seem like less of a big deal that a great guy like you is going to go there for Rapport.
Or, to take your example, if it's actually important that the Countess of Lyndham be convinced that the food was delicious, which isn't true, then you have to use Deceive. If the important thing is successfully navigating the social situation, then you can use Rapport, say, by complimenting the presentation or choice of ingredients such that the Countess of Lyndham doesn't care that you didn't directly answer her question.
The more suspicious someone is or the more specific their demands are, the less likely it is that you get by them with the soft fuzz of social grace and the more likely it is that you have to draw a lie and clash. But hey, even if that's the case, the advantage two-step is there to bail you out - when someone's trying to do something helpful but it won't drop something in one go that's supposed to get dropped in one go, they can Create an Advantage and make it easier for the person who actually tells the lie to land it clean.