I see. Well, I would have to believe that unless you were earning a lot (several thousand) of money from credit card rebates, they probably would not bother. The return on their time to investigate would be very low.

Generally speaking, I believe the IRS has said in the past that cash back is a reduction in tax basis, in case you ever decide to sell what you bought in the future. But I am not sure if they have stated what is must be applied to, so in theory, you could reduce your personal purchases by the aggregate total of cash back (including those earned by company purchases).

If the IRS decided to go after it, it would be a nightmare and they would have to provide a lot of guidance. I thought just of the example where it's a CitiCard with TYN. Points aren't taxable, but you can redeem points for cash rebates on your credit card statement (or mortgage or student loan payments). Does it then become taxable, or does it remain free from tax because it was first earned in points? A lot of unknowns.