Antonyms for the word "over-charged" could include words like "undercharged," "fairly priced," "reasonably priced," and "appropriately charged." These words imply that a service or product has been priced fairly, without any additional fees or hidden costs. "Undercharged" suggests that the cost is lower than expected, while "fairly priced" and "reasonably priced" indicate the cost is appropriate and justifiable. "Appropriately charged" suggests that the cost matches with the value of the product or service provided. All of these terms imply fairness and transparency, which are key elements of good customer service.