While working for my real estate company three years ago, I started a side business as a property manager. The business was slow in the first year but picked up afterwards and I started earning a decent regular income through it.
It never crossed my mind to file the tax returns for the side business. Somehow the IRS found out and they sent a collection notice with back taxes for the past five years, even though I had only been doing it for three years!
My employer uses Legacy Tax & Resolution Services and I contacted their service to help me out. They asked me to provide complete details of the business as well as salary income. They calculated my tax obligation which was much lower than the bill the IRS had sent.
The tax firm helped me file the amended returns which got accepted by the IRS. I now rely on their service to do my taxes for me every year.