there is no way to correctly track sales resulting from your efforts. especially non-internet or different-computer orders and time-displaced purchases cannot be attributed to their origin in large part...
True. Tracking can almost never be done perfectly.
..so you will be cheated
NO. A site owner looks at how a program works and makes a decision to join or not join. That's not being cheated. You get regular reporting of clicks and earnings, and make a decision to stay with the program or drop it. That's not being cheated. As always, it's about the bottom line.
Affiliate marketing is different from simply generating pageviews, and a lot of people here are probably not very far along the learning curve. But it's a valid model that is well-established and can be extremely profitable. Google might end up implementing it badly, or even by forcing publishers into it against their will which would be the nightmare scenario, but the concept shouldn't be dismissed out of hand.