Great question. We've been finding locals a bunch of different ways. A TaskRabbiter suggested we try Craigslist like they did, and that was extremely successful. Locals verify their identity through Stripe on the site, and then we approve them if we like their profile, so we've been able to get some great locals that way. We're also working with local bloggers to reach out to their network, and we've had some success there.
As for the travelers, we're targeting lots of specific groups - football travelers, conference travelers, etc. People we can target.
And we solve the trust equation the same way AirBnb has - reviews, and detailed profiles. We hope the traveler can get a good idea of who they're planning with before they open a plan that way.