A friend of mine who works in the post office says they will give about 50 grams leeway if it is one that has gone into the post box out front, none if handed across the counter - they are obliged to charge the correct amount.

You could risk it and send it by posting in the red box out front but if picked up and weighed they will send you a bill for the parcel rate of the item (usually a lot more than the satchel price) plus a service fee for processing the article.

I have miscalculated on price on occasion, you just have to wear it, it is not the buyers or Australia Post's fault if you don't estimate correctly.

Jenny