Whether or not you choose to call it a "mistake" and how you handle it depends entirely on the business model, image, product, customers, etc.... A recurring s

Whether or not you choose to call it a "mistake" and how you handle it depends entirely on the business model, image, product, customers, etc.... A recurring service that is purchased, where you priced things too high and saw prices drop off, and then quickly moved it back - telling the customers who paid too much, and who would likely get pissed and leave when they find out you were unlucky represent an opportunity to market yourself - saying "Hey, we over did it a bit - we're crediting what you already paid forward at our new reduced rate, and keep charging you at that rate going forward, we appreciate your business!". If anything, that's going to make your customer who was willing to pay double what you are now charging him happy, and spread the word. Who doesn't like to find out they just got a 50% refund?