For me you can't look at the selling side of things in isolation. It's also related to the fact we often initially overpaid for some players and also the massive wages they're on.
Also, i think it's unfair to judge the fees we're generating for players we obviously need to offload with the fees other clubs are getting for players who they don't want to offload. It's a nice problem to have. We're pretty lucky that the likes of Kompany, Zabaleta, Aguero, Silva and Toure (though he had a good try) haven't forced moves away. We've held onto our best players when they've been at their peak, something which other clubs have struggled to do. It's pretty impressive really. Our selling record could have been better but it would have meant losing some of our best players. Everyone cites Daniel Levy as some kind of genius but let's see how much he'd have got for Javi Garcia and Jack Rodwell! Paulinho bought for £17m and sold for £9.9m. Soldado, bought for £26m and sold for £10m. The root cause of bad selling is often bad buying.