Well, it seems that I was not alone in seeing a drop in sales. Around 4th July weekend, my sales suddenly tanked. From 12-15 a day and a high of 19 on one day, it just dropped to 3 or 4 a day.
I just assumed it was a summer slump, or because of the holiday. Didn't seem like I could do much about it, so I concentrated on adding new features, trying to make it better and working on other apps.
Then I finally found this:
So everyone else is having the same problem, all from around the same time.
And it seems to be tied into Search Terms. In my case, if people are looking for a cube that shows photos or pictures, they are most likely to search for "photo cube". Despite me having that exact text in my description, searching for "photo cube" doesn't bring up my app.
Searching for "photocube", "photo kube" and "photokube" are all fine, and return my app in the listing, but they are all less likely than the simple "photo cube" which doesn't work. So I think what happened is that Google changed the Search algorithm at the start of July, and my app suffered. Everyone else is reporting the same problems. In many cases even searching for the exact name of their app is failing to return results. There is also a significant difference between searching on the Market App and on the Market web portal.
Frankly, the Google Market is laughably poor, and breaks at the slightest opportunity, with little redress for developers. Almost every bug report or comment is ignored or answered with standardised replies that don't respond to the issue concerned.
Just this morning, my app ratings have been halved in the Market, I went from 22 to 10 for no apparent reason. That is just completely shit.
So in an attempt to resolve my search issue I have renamed to Photo Cube Live Wallpaper. This now at least returns my app when I search for "photo cube" on the Market Web, but still returns nothing on the Market App on my phone.
So will see what happens over the next few days.
Google Market, not impressed! 2/10, must try harder!