It's strange - according to my reports, I had no orders over a 1 month period, but was still paid $52 for that month.
Was I paid because I delivered so many impressions and Amazon is paying for showing there logo/ad - kind of like how CPM ad's work - where you get paid whether people click or not, just for displaying the ad?
Or does Amazon ONLY pay commissions when someone buys something, and there was a mistake of some sort in the reports?
They might be paying you for accumulated commissions from prior months, if during that time you made sales but had not reached their payment threshold. Also, their payments can be sent out about 2 months after your accumulated commissions exceed the payment threshold, if I'm recalling that correctly, so you might have to look farther back to find the sale.
As far as I know, they pay only for commissions on orders actually shipped, and there is no type of CPM advertising arrangement that I know of.