How do social venture firms make money?

If you are talking about NGO's then the money comes on donation spent on social causes. They collect it through some marketing or personal collection. Also once they are known in that location, corporates, individual voluntarily offer donations which are being spent on social causes. NGO or social venture objective is not to make money for any firm or individual.  .If you are talking about making money through social venture and then all the way it is different, these are small parties, school fetes and even in these events one normally say that50% money will go to charities, etc. If any other type I would live to see any other response.