I received a question about why it seems businesses can make fudge in all sorts of climates whereas most home recipes recommend only making it during dry, cool weather. I have done a smidge of research and come across two articles about making fudge at home.
The main points for making it at home seem to include: the sides need to be rinsed down to prevent sugar crystals from forming, don't stir too soon or sugar crystals can form, and don't let anything fall into the fudge because sugar crystals can form around it.
This applies to commercial operations as well however, these businesses have an extra trick or two up their sleeves. They often use variety of sugars to help ensure that crystallization is unlikely to occur no matter what the conditions; corn syrup is a common one to use, marshmallows, marshmallow creme are another couple of options. There's also the trick of using cream or evaporated milk to prevent curdling.
Anyhow, here are some links that go into more detail. Enjoy.