[throwaway23234]

The thing that killed craigslist was a bunch of startups that took it's ideas and charged 5% for the transaction and lip service about how it is safer than "other platforms" (other platforms being craigslist).

Not saying that's good or bad, but that's what killed craigslist.

[mistrial9]

I doubt this -- starting means developing the user experience (phone friendly probably) and also getting people to hear about it (marketing). Both are hard, what you say is the easy part.