I just discovered something today after moving around a dressing room: If you have the dressing room and the register sharing the same space when the customer comes out of the dressing room, they will leave with a broken heart. I guess it has something to do with them being unable to turn to access the register. I haven't tested it, but I would guess it is probably the same for the mirrors.
So just make sure the space directly in front of the register is not touched on any side by a dressing room or mirror. Hope that helps someone!