The Sea Wasp (Ryk E. Spoor)

Sure, they know there's a saturation point. But they don't care because it's all a numbers game. If you ask enough people to give you money, some tiny fraction of them will say yes. Ask a large enough number of people often enough and the amount of money you can obtain makes it worth the effort--and the less it costs you, the truer that becomes.. And that's doubly true if they don't give a tinker's damn about how many people they aggravate with robo-calls in the process of finding the tiny proportion of suckers who will hand over some cash.