Stores do not sell devices to slow electric meters because tampering with an electric meter is illegal and dangerous. Possible penalties for electric meter tampering include criminal charges both for theft and meter tampering, disconnection from electrical service and fees for meter replacement.
Online advertising touts power factor optimization or correction as a way to save on electricity without meter tampering or reducing power consumption, but these devices do not work. Also called amp reduction units, the claim is that these devices correct household electrical measurements for real use rather than electricity lost through inefficiency. Residential electrical billing already accounts for this, so these devices do nothing.
Electric utilities detect meter tampering through meter readings and by comparison with the average electrical use in an area. Modern digital meters signal anomalies in readings automatically, both to guard against tampering and to help customers receive reliable service.