WhatsApp Scammers?

In places other than Numista I've noticed a lot of coin related posts attracting demands that the OP make contact via a WhatsApp number. Not just sales posts, I mean anything loosely related to coins. I posted a few images of my Wiemar Republic commemoratives in a Facebook coin group and got absolutely spammed out. It's the usual suspects, from the usual countries and the usual hysteria and bad spelling.

Often someone will simply comment "LOL scammer". OK so it's a con game but how exactly does it work? What's the significance of WhatsApp?

While the chances of me actually dealing with "those types" are non existent, I'd still feel more comfortable knowing how the game works. Forewarned is Forearmed! Thanks in advance to anyone who can shed any light on the matter.