The Stranger
The Blue Fairy tells Geppetto the same information about the curse that Rumple said, back when he talked to Charming and Snow from his prison cell.
In SB, the information August provides Emma reiterates everything the BF and Rumple have said about the curse. These separate testimonies, from independent sources, confirm that Rumple can indeed see the future, at least in part, and that he tells the truth in his deals, at least most of the time.
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