Most people ignore incoming whatsapp messages from unknown ID (i.e. not already on your agenda). I would never accept an inbound message from a person not already on my list, and would probably result to blocking the number altogether (straight off). I hardly even pickup calls on my landline or mobile that are not on my agenda, and those identified as private are always skipped. I'm pretty antisocial on social media, and not a spice curious as to what anybody has to offer.