Sims won't buy from display cases (business & hobbies)

Sims will only buy items marked as "for sale" sitting on a surface (table, counter etc). My sim "can" use their selling wiles and occasionally get them to buy from the display cases and stands...but otherwise the customers completely ignore them.  I am trying to use the display cases that came with business & hobbies and have my sim run a bakery/cafe.