It really depends on how they do it. My friend Beth posted around six months ago 'Hey guys, I'm selling Avon now, send me a note if you want a catalog or to place an order, here is my webpage.' and as near as I can tell, that's the only post she's made about her business. Another friend of mine posted a while back that he was now doing freelance graphic arts, and occasionally posts something he did that he is particularly proud of, but otherwise, no further advertising. Another friend is a seamstress and does about the same - occasionally posts a picture of something she thinks turned out better than expected or that was particularly complex - but no 'marketing' via facebook.
With another individual, all she ever posted was 'I'm selling X, buy from me, earn $$$$$ by being my downline. I defriended her and moved on.
When it comes to people in the middle ground, I usually just hide the feed or add them to a group that doesn't invade my feed often.