We Want To Send A Legal Warning Notice

We are an ecommerce startup business operating our services in India. There is one person who didn't buy any services from us but still, they criticize and disgrace other customers and pressurize them by creating a mental pressure by repeatedly disgracing our services and products and preventing them to buy from our website. We want to send her a legal warning notice that if she continues the same practice which is totally wrong on every ground we will file a lawsuit & sue her. We welcome and accept negative reviews and criticism from our customers but without buying anything or having no bad experience with us we don't think it's ok to disgrace our business reputation. So we want ur suggestion for writing this legal notice on the behalf of our business with a warning that next time we will file a lawsuit and will sie her