Unfortunately, not many people leave harsh feedback because they think it not nice or something. All they do is make a post in Trader's feedback about their situation.
Uh, I think most people don't leave harsh feedback because a vast majority of deals end up being smooth, with everything meeting expectations of both parties. That's not unfortunate at all.
In response to the picture requirement, I think it's a good thing. It will force people into requesting more pictures, which will end up with an even higher percentage of happy customers. Even before this change, it was a good idea to ask for more pictures, as most people only posted a zoomed out photo of everything they're offering up. If I ever questioned a yoyo, I'd always ask for better pictures. Now this behavior will just be business as usual.