Just re watched Price of Gold, there were a few things that tie in here.
1) Rumpel told Cinderella that the magic wand was pure evil, and that all magic comes with a price. So are fairies playing around with good and evil in their use of magic, trying to use evil for good? Maybe fairies are only supposed to be fairy dust shakers like Tinkerbell, and they have expanded into other magic.
2) The mines are no longer in use and have been converted to a special place to hold Rumpelstiltskin. So is fairy dust no longer needed?
3) The quill used to freeze Rumplestiltskin had a spell put upon it by the blue fairy. No fairy dust involved that we know of.
and 4) Cinderella questions using the quill since she has learned that all magic comes with a price and feels that is what has gotten them into trouble in the first place; to which Thomas replies he is willing to pay the price to save her and the baby. So I am wondering if his disappearance is the price paid for using the magic quill? ( for comments on that topic visit https://oncepodcast.com/forums/viewtopic.php?f=7&t=226? ) And so if the fairies do help using magic is there a price for it like Rumpel said in this other epsiode? I was assuming fairy magic wasn’t costly in that way, but in fact freely given for helping the people of FTL.