Sadly, the answer is "lots of broken souls". Picture for sad, sad proof- this is just a
sample of the groups that show up when searching "used panties" (which also picks up other used underwear oddly enough) on Fet. That's not including events, or profiles doing it directly. And look how many members there are in these groups.
Yep, I've heard that too from one or two girls I knew who sunk to that particular brand of sketchy moneymaking. Even if you do dirty them yourself, as it were, you still buy cheap stuff (I'm talking the ones you buy of all the same colour in a bulk pack for a couple bucks) and mark it up...in more ways than one.