I realise that some charity shops aren't allowed to but i think some shops must lose quite a bit of business by their outright refusal to accept a "knock down", usually saying "we aren't allowed, it's a set price" sort of thing.
I wonder if that's always true, because recently i asked if they'd take a bit less on some walking boots which i thought were a bit dear, got told "no we can't" then i noticed the brand new price underneath theirs and it was only about £2 less brand new. When i pointed it out she said "well if that's the case I will reduce them for you" . So she did have the power to reduce after all.
So when they say they can't reduce, maybe in a lot of shops they can if they want to?