Why do you consider this income?  Because it's shown on a piece of paper?  But we know that the Internal Revenue Code of 1986 enacts a tax on income, not on pieces of paper.  

Let's say I'm walking down the street and see IronMan, who owes me $100 for a used anvil I sold him last week.  He pulls out his wallet and starts to hand me a Benjamin.  But a thief runs by and yanks it out of our hands just as the transaction is about to be completed.  Do I have income? Do I have a deduction?  Does he still owe me some money?