I don't. They'll simply not bother with selling to avoid the risks. I've seen people stockpile ridiculous amounts (and thus waste a lot) out of fear of droughts, in realms where it never will be an issue.
I don't have a problem with people stockpiling insane amounts for IC reasons. The cities will starve for those IC reasons. It's all good.
The problem is when people stockpile food not for IC reasons, but because they've done all that could be done with food and get bored.
