I don't really get why they're focusing on the demand-side. The "Wanted" section of Craigslist is considerably smaller than most of the other For Sale categories (I personally never check it).
I also don't see any real-world/brick-and-mortar example of reverse person-to-person selling like this. What is the incentive for someone to even check Zaarly for a need I might meet? Don't say "make extra cash" because if I need to sell stuff, I dig through it and post it for sale.
If I need something, I search Craigslist. If it's not there, I check Ebay. Or I buy it new. I don't post a request and pray someone will get back to me.
People are going to request things ... and most requests will go unanswered. Then they'll stop using it.
(BTW, totally not trying to sound like a pessimistic jerk)
I'm in DC right now and can only find 4 items within a few miles. I think that kind of experience will give people a bad first impression.
Anything location-based needs to start in 1 or 2 cities and grow from there–until other cities are begging for it.