This simile contains the one instance of the adjective alēthēs in Homeric epic that is not applied directly to verbal communication, but to a person, a woman weighing wool with scales. The other instances of alēthēs show that it qualifies (the content of) speech, indicating that it denotes truthfulness in the sense of not forgetting what has been said in an uninterrupted continuum of time, and not letting anything slip by one without being mindful of its implications (and indeed, a-lēthēs and a-lētheia are to be understood in opposition to lēthē). Here, however, it can be seen to be applied by a logical extension to the agent of such communication, and so, to indicate the woman’s scrupulousness in her business transactions (so Cole).
Insofar as the simile and the wool-weighing woman illustrates the balance of the battle between the Greeks and the Trojans, there is a further dimension to her being alēthēs. The balance of and then the change in a battle is often represented through the image of Zeus weighing the two sides in scales (e.g. I.8.69-74, I.16.658, I.19.223-224, I.22.209-213), and this image of Zeus can be seen to be implied here, too, even if it is not explicitly presented as such: in lines 437-438 Zeus gives the upper hand to Hektor. Detienne argues that this image reflects the idea of the archaic king pronouncing justice, with which scales are likewise associated: such pronouncements of justice by the king are just and alēthēs. The model for this king is Zeus in his role of administering justice and judging between two sides, using his scales – and so the adjective is appropriate here, too, signaling the divine justness and alētheia of the judgement weighed in the scales. The application of the adjective alēthēs explicitly to the woman within the simile, then, presents her in the role of Zeus as a divine judge, transferring to the vehicle an attribute of the tenor. And the idea of pronouncing such judgements brings alēthēs here, too, back to the sphere of communication that excludes forgetting, ignoring, and failing to notice by its opposition to lēthē.
See further:
Cole, Thomas. 1983. “Archaic Truth.” Quaderni Urbinati di cultura classica n.s. 13:7-28.
Detienne, Marcel. 1973. Les maîtres de vérité dans la Grèce archaïque. Second edition. Paris: Maspero.
_______. 1996. The Masters of Truth in Archaic Greece. Transl. Janet Lloyd. New York: Zone Books.