If you got a CP2000 letter, it compliance letter kicked out by a computer. It usually is very specific and indicates what caused the audit. Unless you _know_ you are right (and have legal advice to back it up), dont challenge it; just pay up.
I trusted TurboTax, which missed some investment data. TurboTAx downloads data from investment firms, but in my case the data was incomplete. The IRS letter said I owed $7000 and to respond in three weeks (just before April 15th.) A friend accountant completed a response with the advice to send as little as possible. They didn’t like “little” and affirmed the first notice. Now that it was after June 1st, I hired a good accountant and he completed all the forms, called and faxed them to the IRS. I’m awaiting a response, but will appeal before the 90 days is up if I don’t hear.
I prefer honesty, so I’ll tell em what ever they want to know.