They usually sell absolute cr@p, musically speaking, in Edinburgh Woollen Mill shops (which do pervade across the Border - even one in Sidmouth, Noreen!) Think I'm sounding a bit like Jack there too!
But they do have the odd gems: but if you don't know your quality stuff from your "all at 120 bpm singalonga Scots songs with chicka chicka beat CDs" you could buy something you wouldn't give to your worst enemy.
If you are in Edinburgh, go to Coda Music on The Mound for a browse: you will find a great selection there and probably come way penniless. (No vested interest I assure you, just a very good shop!)