I tried to do the demo, but was asked for an email address. While I trust that you won't spam me, I don't understand why I have to provide an email address for demo purposes. If you are going to provide a demo, I would recommend either doing a video, some screenshots, or have a demo that doesn't require any interaction from the end user.

I think the problem with your homepage text that others have noted is not so much in stating the concept of the problem the app solves, but really in stating what the benefits are to both the buyer and seller. Most suppliers are going to understand economies of scale, but many buyers are concerned more with end price. You have to convey to the buyer WHY economies of scale is better for them. With that done, you also need to convince suppliers that your app will increase sales for them.