Here is a quick list of the small business tax deductions that the IRS cannot stand. That isn’t phrased correctly. The IRS actually likes these tax deductions since most business owners either incorrectly deduct them or cannot substantiate an otherwise qualified deduction for lack of proper record keeping.
The IRS plays pot odds on the following business deductions since the recovery of taxes is probable and therefore profitable for the government. In poker, if it costs you $10 to bet and there is $100 in the pot, then you can be wrong 90% of the time and still break even. This is the essence of the pot odds: You're paying a fraction to win a larger sum, and the IRS is no different.
Here we go-
There are others, but these are the biggies. This should not have a chilling effect on you deducting these expenses. You should not be afraid of an audit. You should not be afraid of losing an audit. You should only be afraid of having an unreasonable or indefensible position. Sure, easy for us to say.
At the same time, if you have legitimate expenses and you can back them up with proof, then happily deduct them. Like Muhammad Ali once said, “It’s not bragging if you can back it up.” Well, the same can be said of small business tax deductions that are at higher risk of audit. If you can back it up then deduct it!
Taxpayer's Comprehensive Guide to LLCs and S Corps : 2019 Edition