"undeceiver"?

OK, not ideal, and slightly esoteric, but:

• rolls of the tongue
• parodies "unbeliever"
• just odd enough to get attention without being impenetrable
• has nice-ish connotations insofar as it implies that you won't deceive others, and thereby avoids exclusive focus on the self.
• fits with the "less wrong" tradition of understatement: trying to be less (self-)deceived, rather than claiming truth