But on the other hand Etsy4Farmers (tm) would probably turn out like Etsy, and care progressively less about the farmers, more about money and eventually turn into just another online supermarket riddled with fake products and fake reviews (not suggesting Etsy has made it all the way there either btw).

This guy has one partner, Incentives are aligned, if I were one to buy onions online, I can see myself still being happy with them in 20 years time. Maybe it cost more, but they don't have a monopoly on Onions, their ability to pass on that cost is limited, which is the major concern, is it not?