I agree. With the help of a demo you can study the response of the public and get many important parameters for the project in general.
I think that the demo showed real mechanisms of interaction between sellers and buyers, it will be necessary to sell something on it and buy something. Probably the most simple - crypto-currencies.
This option is possible. But it is even simpler to launch a contest in the framework of a special campaign (with payment to the best participants), which will require the commission of such operations.