That's why you (in addition to all that has been said) should make very clear how easy it is to up- and downgrade. Also there could be small hints next to the

That's why you (in addition to all that has been said) should make very clear how easy it is to up- and downgrade. Also there could be small hints next to the slider (yes, I'm a fan of sliders;)) as it snaps into the various positions... But those are again just ideas. You should get a good designer on the case, this is their bread & butter.