The government gives a REC (renewable energy credit) for each lightbulb installed (or each household, not sure which) to the installer. These are like tradeable securities usually sold to a "rec bank" effectivly these rec banks are stores for electriciy companies and the like to purchase recs to ofset their carbon emissions.
http://www.green-bank.com.au/
The same applies to solar generation units and solar hot water units. My solar power unit generates 4 recs each year. (i think thats right). These are generally signed over to the installer in return for some kind of discount on the installation or product.
STAY AWAY FROM DOOR TO DOOR INSULATION OFFERS.
shoddy workmanship has led to a number of house fires. If you want insulation installed, contact a reputable company.