Tony I have fitted a lot of second hand carpets refitts,especially now people are tightening their belts , and what people dont realise which we always tell them before hand is carpets will always take the shape of the room they were in ie lumps bumps ,and they will have crushed pile were perhaps units beds etc were and this will not come out ,also you would be surprised how the sun bleaches carpets so consequently when you refitt them they look awfull with patches everywhere .A carpet will wear by a door or in a heavy walk area so if you then fit it in a bedroom off a wall for instance it will look as if it is dirty which is in fact carpet wear.I could go on and on but wont bore the pants of you,but will reitterate that a second hand carpet will never go down or clean up like one that has been specifically laid from new for that house,unless of course it has only been down for a very short period and even then it would have problems imo .So dont beat yourself up about it ,and the cant polish a turd is very apt ,which I nearly fell of my chair laughing about ,need to remember that one.