It's just happened again. I bought "Air Display" by Avatron on 8 July. I played with it and unfortunately discovered it was not able to play an .avi file from a PC on the iPad as secondary monitor. Not only that, the PC display stayed messed up even when Air Display wasn't running. There was suddenly a whole area of invisible virtual desktop (lost mouse, strange remote display).
I tried posting to the Avatron forum, but the relevant technical forum is read-only (?). So I contacted Avatron and they offered a couple of suggestions that were not able to solve the problem. All I ended up with was a bland "No, this is not a known issue. We'll certainly look into this and see if we can reproduce the issue."
So today I ended up contacting iTunes. But they referred me back to Avatron because it was a technical problem. So I asked Avatron for a refund, but Avatron replied "If you'd like to pursue a refund you'll need to contact Apple." But as soon as I tried to return to the relevant iTunes link I was informed "U hebt al een probleem gemeld met dit artikel, of het is te oud om te melden." No idea why Apple still insists on addressing me in Dutch to inform me that I had already reported a problem, but that's obviously Catch 23.
Or course writing this blog costs a lot more than €7.99, but that seems to be the Apple strategy to stop complaints. Make it more expensive to complain than to shrug your shoulders and put up with it.