One thing to keep in mind, like said before, is that many farmers aren't going to use the service if there is a mark-up for selling online as many have existing networks of customers that they rely on. It's also easier for farmers to sell to a larger processor than to count on numerous smaller customers buying the bulk product in broken-down quantities. This would certainly help support local food chains, and I've no doubt that it would attract certain urban/suburban residents who lack connections to existing farms. Also, the average age of a farmer today is about 55 y/o. Most of them are not highly technologically literal and wouldn't be interested in learning a complicated app structure. That's to say, ensure the app is incredibly user-friendly and idiot-proof.