RE I've got a sister-in-law -- who doubled her business by inviting her friends (and their friends) to visit her booth at a holiday gift show which benefited her local historical association ...
Again, I have no argument with like-minded people interacting in this fashion; it's not the same as strangers doing so.
My point is that I would never respond to such an offer unless it was a personalized (and I mean really personal) contact from a trusted source.
And I will forever remain leery about the seamy qua destructive side of "social media". Caveat emptor. Caveat lector. Caveat utor.
