Granted, (B) is a side issue, but I'm surprised that you could have been doing philosophy so long and still claim that fairies don't exist. The following Quine style criterion of ontological commitment seems unobjectionable:
For any true sentence of the form Fa, the singular term "a" must have a referent.
So, for example, if it is true that Debussy is awesome, then "Debussy" cannot be a vacuous term.
But, we have true sentences of the form Fa whose singular terms purport to refer to fairies. For instance, "Puck is mischievous", "Oberon is a jerk", and "Ariel is a lacky" are all true sentences. We would accept them, while ruling out others such as "Puck is the Prince of Denmark" or "Oberon was the auther of Waverly."
But then, according to the criterion of ontological commitment, fairies exist. QED.