If the products don't sell at market, you have set the price too high. Go back to the market and reduce the price of the products which have the highest demand until they start selling. Later in the game when you have lots of products at the market and they suddenly start selling quickly, your prices are too low and you should go immediately to the market and raise the prices of the products which are selling quickly. Nothing happens at the farm while you are at the market, so stay as long as you like to optimise your prices. Green is too cheap - Increase until yellow and go up another couple of clicks for optimum selling price.