Irregular reinforcement is a hugely powerful message sender.Last year, I called it surprise rewards. If it's too expensive to surprise and delight every customers every time, surprise them randomly. Send one of them a remarkable gift for no reason at all.
The reason surprise rewards are so powerful stems from congruity theory (which also is the primary reason you shouldn't choose a descriptive name for your brand). Congruity theory states that encounters incongruent with expectations cause people to apply inordinate mental effort to resolve the incongruency.