How does the IRS know I’m being accurate: If you received 1099’s for your work, they also received them. They will know if you omit income, unless it’s cash. I don’t recommend not reporting your cash because 1. It’s illegal and 2. You have a growing business and should be proud of your income. If you ever want to purchase a house, car, etc. you need to be able to show proof of income and that’s what your taxes are. As far as expenses use the honor system but keep in mind you need to keep records in case of an audit. Speaking of audits, they are very rare and the IRS is TERRIBLY understaffed. Not even worth thinking about in my opinion. As I mentioned before just keep records and receipts just in case. Since you’re doing your first Sch. C you should probably use a service like TurboTax, they make it dummy proof and they have live agents that you can chat with or call when you have questions. Some people hate TurboTax, I personally think it’s great especially for beginners. Good luck!