Schedule c Writing off losses

you only get to deduct a business expense once.  thus if you deducted supplies you can't take a theft loss.  if you expensed inventory purchases you can't take a theft loss deduction. if you expense the cost of repairs you can't deduct them as damages.   if you haven't otherwise deducted what was stolen, then the next questions are do you have insurance and if you do did you file an insurance claim?  the IRS will disallow losses covered by insurance. 

You can deduct your actual costs to repair your business property.  In some cases, if you improve your property, you must list the improvement as an asset and depreciate it.  

If inventory was destroyed or stolen, you can't do anything else.  You already deducted the cost, you can't deduct it again.  Your "write off" is that you don't have taxable income to report for selling the items, so your income is less.  If your inventory was reimbursed by insurance, that is income, as if you "sold" the items to the insurance company (although probably for less than full retail price).  

If property assets were destroyed or stolen (items that are only partially depreciated) you can report them as destroyed or stolen, and claim the remaining depreciation.  If you receive insurance reimbursement, you must report that, and that may actually cause taxable capital gain income.  (For example, if you had a bakery oven that was fully depreciated, and you receive $5000 insurance payment, that $5000 is taxable depreciation recapture.)  I believe Turbotax will ask about insurance coverage for destroyed or stolen property, or you can report it as a "sale" to the insurance company for the amount of reimbursement.  

If you have insurance coverage and don't use it, the IRS will disallow any losses that could have been covered by insurance.