im sure that there not atcherly "second hand" but like where main shops who order in mass i.e tesco may over order and then either send um back or sell them onto "Quality Seconds" for a cheaper price then QS pass the savings onto you. ive only ever been in QS once and noticed that some of the clothes do look a bit rough and there could also be minor mistakes (stiching, transfers, etc.) and then instead of throwing them away they send sell them to QS (only the ones which are very minor mistakes.)
hope that helps.. sorry if not much is understood :P