I'm sure some freebie hunters do end up buying but I'm guessing most of them go to all of the sites so they can build up their free image inventory and rarely buy.
I dunno man. I've taken a look around at the freebie stuff. It's really not that great. Keep in mind, that not only are they offering essentially "rejects", but the
search engines for these sites BLOW. The first reaction everyone has to them is "WHAT! FREE IMAGES!?", but they always fail to really investigate the
buyer experience. They are getting more than just low cost images when they pay, but also search engine creature comforts.