If a staff member has created a poor display, left the shop untidy or done something else wrong that is easily captured by photo, take a BEFORE photo, tis it and take an AFTER photo.
Place both photos on a noticeboard in the back room and explain the difference. Be clear why you want the look of the AFTER photo and what it means for the business.
Sometimes telling someone to do something will not be as well understood as if you show them with the type of photo example I suggest here.