The first guy is indecernable. Regardless of what he is he will say he is a good-guy. As Ellis said the second is lying because he said the first said hes a villain (which is impossible). The third said the second is lying (which he is) making 3 a GG.
1st - Impossible
2nd - Villain/Liar
3rd - Good Guy/Truthful
ellis, right answer but I didn’t follow all your reasoning.
I would say, A either is telling the truth or not. If he is, then B is GG and telling the truth when he says A is not GG. In this case A is telling tyhe truth but is not GG.
If A is lying, then B is not GG. B, however, is telling the truth when he says A is not GG. So in this case B is teling the truth but is not GG.
Your version is a little more lucid, but we followed the same chain of logic.
-ellis
btw, TTnGG = Truth-Telling non-Good Guy
Another solution to the 12 coin, 3 balance problem is to code the coins using base-3 numbers. There are 27 possible 3-digit base-3 numbers using the digits 0, 1 & 2. Pick a set of 12 of these with the following properties:
(1) The set of 12 has four numbers with 0’s, four with 1’s, and four with 2’s in each of the three digit positions, and
(2) The “digits complement” of a number in the set cannot also be in the set (where “digits complement” is defined as the number obtained by replacing all 0’s with 2’s, all 2’s with 0’s, and leaving 1’s alone).
One such set is 001, 012, 020, 021, 100, 102, 112, 121, 200, 211, 212, 220.
Code the 12 coins with these numbers.
Now conduct the 3 weighings. For the first, place the 4 coins with 0’s in the first digit position on the left side, the 4 with 2’s in the first digit position on the right,and leaving the 4 with 1’s aside. Repeat for the second and third weighings, using coins with 0’s and 2’s in the second and third digit positions. After each weighing record a 0 if the left side is lighter than the right, a 2 if heavier, and a 1 if the sides balance. You end up with a 3-digit number. If that number is in the original set, the coin coded with that number is the odd one and it is light. If the number is not in the set, its “complement” is, and that coin is heavy.
Try it, you’ll like it.
ellis–You lost me early on when you said " A lies (is a V)." No matter, your answer was correct.
Try another? Same source as the last.
This time all speakers are either GGs or Vs.
C says: "B is a V.’
B says: “A and C are of the same type (both GG or both V).”
What is A?
Re the OP…
Perhaps the OP misquoted the original puzzle, and it should have been, “What five-letter word doubles when you add two letters?” [Note the slight difference]
'Cause if that were the case, then the answer could be DOLES. Add a UB, and you get DOUBLES. Well? Whaddaya think?
A possibility – although it would be a bit less awkwardly phrased if you instead posed the question thusly: “What five-letter word is doubled when you add two letters?” – with the correct answer then being “doled.”
It works – but still seems kinda cheesy.
Ablett
I think you missedc the last paragraph:
A is a villian. If C is a villian, then B is a GG. If B is a GG, then C and A are the same(ie both V’s). If C is a GG, then B is a V, and C and A are opposites, meaning A is a V either way.
Inbox. Assuming my inbox has two ‘letters’ in it already (it could be a good old-fashioned inbox, not an email one), then if someone adds another two letters my inbox will have doubled in size.
Or is this just too tortuous?
Oh, Reuben!
Tortuous and torturous.
Was it really worth becoming a Straight Dope member for that? 
Creative…however if it’s a “good-old fashioned inbox,” then your inbox won’t have doubled in size if you add two letters…merely its contents.
You might get away with this if it were a virtual inbox you were discussing. However, I still favor a strict construction of the language of the OP. As I stated long ago, the question says THE WORD doubles in size…not the object/concept/whatever the word refers to.
Given this, the “doled/doubled” answer may be as good as it gets (assuming we allow the original question to be rephrased slightly).
Arf! It sure was… I’ve been intermittently lurking the SDMB for months; I was just too busy to get round to subscribing, etc.
The OP of this thread interested me enough to finally jump in. Pleased to meet you all!
No more lateral solutions have come to me since this morning, you are probably glad to hear… 
– R.
(Reuben is my real name btw)
Hey welcome to the board Reuben
“focus” + “es” = “focuses” A focus is a point. It has zero size, as does any number of focuses (or foci). 2*0 = 0, so this is double the original size.
“folds” + “un” = “unfolds” One definition a fold is an object doubled over on itself. If you have a some folds, and unfold them, they appear to double in size. Ok, maybe “unfolds” is not a noun.
If it is permitted to rearrange the letters:
“scone” + “ds” = “seconds” If you eat a scone, and then have seconds you have doubled the orginal amount.
“moose” + “tw” = “twosome” If a moose becomes a twosome, the total size has doubled.
For those who think the question refers to the size of the word itself, instead of its meaning, some of the above examples double the number of syllables. If you mean size of the displayed word it depends on the typeface, but
“cilia” +“mm” = “mimical” is fairly close:
ciliacilia
mimical