I'll calculate my own taxes thank you very much. If big brother doesn't agree, then I'll show my work and sources. Otherwise, the less they know the better.
No, that's exactly what an audit is. They want to see proof. Sometimes you just need to send a letter to the IRS explaining your reasoning. If they don't agree, and you think you are right, then you should probably get a cpa. If they still don't accept and you want to fight their decision, then get a tax lawyer.
Having also been there, this was not my experience. The IRS sent me a bill for $1500 claiming I had taken an early deduction from my IRA. I had, but it was only to correct a mistake I made right before of contributing too much for a given year. I filed paperwork with my brokerage at the time to reflect this, but apparently the IRS didn't get that.
I replied to the bill with the relevant paperwork and a 1 page letter explaining what happened, and the IRS agreed I did not actually owe them anything. No lawyer required.
The current system is like having to write your own credit card statement, mail it in to the CC company, and getting penalized if you get it wrong.