I am not a full time seller, just a rider who keeps buying and selling. I sell stuff that I don't use anymore but in mint condition, or some brand new spare that I bought but never use. Occasionally I help friend to sell stuff too, provided the stuff is in good condition.
I have no time for nonsense and WhatsApp. The money from selling these stuff is too little for my survival, so to save time for other big money I only deal with serious buyer via email. WhatsApp only comes later when deal sealed.