Couple of things in the listings I looked at. You need to check your spelling, when talking about weight loss it is lose, not loose. You cannot quote postage and then say in the listig that it may be different. If isomething weighs over 500g and won't fit in a then you should use the calculated postage option making sure you fill in the correct weight and dimensions then a prospective buyer will see the cost to their address.  If you are offering delivery yourself is that Australia wide? If so then select freight if you are sending something too heavy or large for Aus Post.