Hi, here is a reply to the same question from the Help Me thread. Hope this helps...

Quote Originally Posted by AnnirasSweets View Post
This is called a Quick Sale and is a result of blocking the door. The game is not meant to run that way so it confuses the programming and all your accumulated food will sell instantly. The way to stop this is to leave your doors opened regardless of your food situation.

The only downside to having no food is that your heart rating goes down. In reality, heart rating has no bearing on your game play; it doesn't alter how many coins you make or points earned or anything - pretty sure it's just a way to let us know we're not currently making coins. And of course, heart ratings will refill within a minute or so once you get food out so it's a very temporary issue.

It's up to the individual player, of course, but I think it's not worth it to block the doors when the possibility of a Quick Sale is always there.