Can one person build a two-sided marketplace?

Only if you already have the crowd. A two-sided marketplace is empty until it's crowded: each side only arrives if the other is already there. Getting both there at once needs an existing crowd on one side, or money and people to fill one side by force. One person building in the evenings has neither.

The weekend call-out

A friend from school became an electrician, and for years he complained about the weekend call-out. Customers rang on a Saturday with a fault that couldn't wait. Sometimes he didn't want the job: his daughter's birthday, already booked, 40 minutes away. Other electricians wanted exactly those jobs. There was no way to pass one across except ringing round, and by then the customer had found somebody else.

So I built a small marketplace. An electrician posted a job he didn't want; another took it and paid a small fee to the one who passed it on. Real people, a real problem, a clever little design. It took 4 weeks, because a marketplace needs 2 of everything: 2 kinds of account, 2 sets of screens, 2 kinds of notification.

Every time I filled one side

For the launch I asked my friend and a few electricians he knew to post real jobs. (I wouldn't fake a listing. That's a line I've never crossed.) So there were jobs, on real Saturdays, and nobody to take them. They expired, and the friends who'd posted them stopped posting.

By month 3 I'd spent my evenings finding electricians who wanted the work. A handful signed up and waited. Now there were no jobs, because the first side had learned that nothing happened when they posted. By month 5 both sides had gone quiet. In month 7 I switched it off and wrote to everybody to apologise.

The day 1 test

Ask of any idea: is it useful to the first customer on their own, on day 1? If it only becomes useful once other customers arrive, write down where those others will come from. If you can't, stop.

The electricians' problem was real. A tool one electrician could use alone, with his own regular customers, might have lived.

Nobody Bought It has the marketplace's autopsy in Part IV.