However, the writing is on the wall for any "sharing economy" service that is simply a technology wrapper for non-SSN'd workers in the US. A couple of challenges that aren't solved by technology:
1. Many unskilled labor positions, especially those that incorporate illegal immigrants, are paid in cash.
2. The price points are absurdly low to create any sort of margin to sustain a business (I can only assume most of these companies are doing < 10% gross margin)
3. Response of workers turns sour when they realize the system inevitably becomes indentured servitude.
4. "Rigorous background checks" - I have yet to see how technology has made background checks any more "rigorous" or how this has allowed companies to scale the quality of workers.
5. Scaling quality - many of these services (moreso for services like Thumbtack) start by hiring skilled people (usually MBA students, aspiring actors, etc) who are looking to earn a few extra bucks for fairly unskilled activities. People enjoy the service since they not only get a higher quality service but also because "it comes with a smile". There is only a limited pool of these type of workers, which inevitably means the supply side of the business gets eliminated at a certain scale.
I think there might be a place for these type of businesses, but perhaps not in the venture world.