Spending tons of time posting and building a following of people who don't buy. Comments, likes, friends, shares, etc. are completely worthless if no one is buying.... This is exactly what my girlfriend is doing. I tried to tell her.
You cannot call it a complete waste of time.... Having a large following does help in promoting articles, blogs or her products. When the right products comes along, I am sure people will buy. Beside you cannot argue with a women.
That depends on the audience. If you build an audience based on memes and videos, you typically have almost zero buyers or people interested in clicking through to an article. There are plenty of Facebook pages with hundreds of thousands of worthless followers.