What would you do, if you purchased a piece of furniture and only to find out you have to..............?

I have ordered a set of dinner chairs from Harvey Norman and when I paid my deposit I asked the sales man to add extra suport to the chairs. Which is a piece of wood beteen each leg. Now he says I have to drill the holes and put them on my self. No matter what the chairs come flat packed. What would you do/say to the lazy sales man about getting me to add the support rails on myself?