> If you read Teaching Introductory Physics the author very clearly points out that there is no way of knowing the direction of the charge

The author is wrong and you also. If people don't know about things then I'd rather have them stay quiet and learn about them rather than spreading misinformation.

DC Current flow: https://energyeducation.ca/encyclopedia/Direct_current#:~:te....

AC Current flows both ways: https://energyeducation.ca/encyclopedia/Alternating_current