If farmers expect to be able to sell tomatoes at $40 a pound at Pike Place Market, they will bring loads of them. If they expect the price to be only $1 per pound, a much smaller quantity will be made available.
I find this to be similar to the thrift pop ups when the weather is nice during the fall semester outside of Ellis. Similar to the farmers selling tomatoes, the clothing pop up owners may decide to raise the prices higher if the weather is nice because they know that more people will see them and more people will be willing to pay a higher price. Whereas vice versa, if the weather is not nice they will not expect many people to come and will lower the price in hopes of making more sells to less people.