one with fish

I was pretty impressed by the price of your cockles..... $10.00 a kilo, so drove to your store and ordered a kilo of Goolwa Cockles, and was told by your assist you don't sell a kilo and was sold a 1.5 kilo bag for $18.00, after double checking the receipt, by my calculations this makes a kilo $12.00, not $10.00 as said, is this a genuine mistake or misrepresentation...?