Also, perhaps you could sweeten the deal to encourage participation as well as marketing? Offer an ____% upvote (based on order size?) on a post by the person filling the order? Require it to be a post linking to the project, and stating that they filled an order for @whateveruseritsfor for the amount of ____SP in exchange for _____ STEEM?

This upvote would offer them a slightly increased return on their investment, encouraging others to participate, as well as spread the good word around in regards to the project by showing that it's working, and that it's a legit way to increase your revenue.