400 food won't feed my city for 6 days. And the offers sit for weeks, and expire unfilled. I literally see dozens of buy offers for prices from 40-50/100, every time I look.
Whats the population fed per 1 unit of food?
My city has a population of 11,300 and requires 23 food per day, or 1 unit of food per 491 people.
Other places are between 394 to 510 people fed per 1 unit of food.
Based on an overall average of 451 people fed per 1 unit of food, 400 food lasting 6 days, your city has a population of around 30,222?