The vetting would have to be really good, though, due to the big ratio of potential liability to potential income. The potential upside is one or two month's rent, but the potential downside is a renter who throws a big party and trashes the place. That's one reason I've never sublet my place when I've been gone--- the $800 or whatever that I'd get for a month absence isn't worth the risk of ending up holding a $10k damages bill. So I'd only sublease through a service like that if either I was sure the service's vetting was perfect, or the service was willing to insure against any damage done by their renters.
My solution (in a cousin comment) is to actually lease to large corporations and universities. They can allow their employees a short term stay at a rate comparable to regular rental in exchange for assuming full liability. There'd still be vetting of the individuals on top of this.
