Not every business is 'sustainable' through repeat customers - funeral homes come to mind. However, if the only way to be sustainable is to break laws, that's where the problem lies.
Sure, but at the scale the ringtone business grew (and burned through users), they eventually ran out of suckers to scam. A lot of them would fold shortly thereafter, or move on to a different market (usually a completely different country), or consolidate with another company overseas and tap the suckerbase there.
This model is basically a modern, bigger-scale version of the old snake oil sales model. Set up a shop in town, sell a bunch of bad merch, get run out of town, find a new town. Rinse and repeat.
Eventually, though, your model catches up to you. Either you're closing up shop in old markets and opening new ones that aren't as big or lucrative, or you're keeping a toehold in the old markets -- but the costs of doing so grow faster than your revenues. Or you flee Market A for Market B, only to have a competitor or two leap into Market B the next month.
Sad thing is, JustFAB seems to be just like these companies. Only it looks good and it is supposed to be a 'legitimate' business.