Dishonest staff - lying at its best

So, what are the chances, second time from same store, pattern? Or is it the way they were trained? My son bought a crossbow, few days later, it broke. I took original receipt to Toys R Us Canal Walk - and guess what, the cashier said that its their policy for them to swap it for a new one as I don't have original box and she will keep the box of the new one. I told her, that the policy if I don't want the toy any longer if it doesn't work, not the policy if it is broken. She pointed out to a poster high on the wall and said I must read, guess what, she ****. I asked, what if I now take the new one, and it breaks in a weeks time, her response \ well