1a) You do some kind of work for someone else, they pay you for it.
1b) You sell something to someone else.
2) The above mentioned someone else reports paying you to the IRS
3) You fail to report the proceeds of sale or work as income
4) IRS bends you over a barrel and rapes you. Repeatedly.
OK, got it. I hire Joe the carpenter to do a small job on my rental house, and deduct the cost as a business expense. His invoice is my proof of the expense. But by using it as that I have a ratted him out if he does not report the income.