There is not other way to signal to the developer that the software is not what you thought it was. For instance, I purchased a note-taking app from the App Store last night that turned out to not be what I needed. There was no way of knowing this beforehand because there is no free version that I could test and pirating it would have been way more trouble than it's worth (plus, I'm not doing that anymore).
So, what's the reasonable solution? For physical goods, if I'm unhappy with the purchase, I can return the item and receive a refund. For software, there is no good return method.
Now, one could argue that it's only a $10 app, but that isn't the point. The point is that $10 paid for something that I don't want or need, and while $10 probably isn't much to me, it should not be yours because your product failed to meet my needs.
As for the rest of the post, the purchaser in that case was out of line. He'd bought the product, used it for a significant amount of time, and apparently gotten some value out of it. At that point, there should be no ability to return the item.