Thieves, fires, and the casino
You can turn thieves off. Since v0.1.57 the switch is Thief spawns, at the bottom of Difficulty inside World Settings. Load the save first. The toggle is not on the title screen. I am correcting older pages that said the option did not exist.
Thieves
The store description says a thief may go for the money in the register, and that you answer with tools such as shuriken. Players on the discussions said that after v0.1.57 a thief could show up several times in one day. The same patch fixed a bug where payments and experience updates kept delaying the next spawn. Frequency depends on the patch and on difficulty. If you do not want them, use the switch rather than a mod.
Fires
Fires are in the store description, and the tool named next to them is a fire extinguisher. Players say the common cause is leaving the stove on when the day ends. That is discussion testimony, not a studio manual, but it is specific enough that I keep an extinguisher in the advice. v0.1.57 also fixed a case where burnt equipment could not be sold until you unassigned the staff on it.
Casino
The store says you can try your luck at the casino and win some cash. The late roadmap adds more gambling content. I do not have the bet sizes or the odds. One review mentioned turning $600 into $900. That is one night, not a strategy, and I would not plan payroll around it.
Questions
Can I disable thieves?
Yes, after v0.1.57. Load a save, open Options, World Settings, Difficulty, and switch Thief spawns off.
Is there a dedicated anti-thief item?
The store text names shuriken. It does not list a full arsenal.