"Market is where you can buy and sell Crops. Upgraded market can increase the volume of trade and restart today's trade."
It important to note the last bit in the quote. Restarting the days trade means that your market trade cap has reset and you can buy or sell with a new cap. Don't forget to buy or sell between market upgrades. The market is available at Senatus level 12.
You cannot sell crops when your amount of silver is over the maximum capacity. There's also Fair tab now which allows u to trade gold for silver or vise versa (fee gold,which means it's bought with real money),also Fair tab can be used as silver storage if u have excess of silver by being away for so long in the game for only a fee 0.5% of the total silver used.
Opens the market menu. This is where you buy and sell crops.
You can buy at the black market for double the price it is offered normally. Since prices change randomly and vary between 0.5 and 2.0 it might be worth buying and selling to make a profit.