Actually, I've found the eBay postage calculator to be just as accurate as Australia Post's on-line calculator, provided that you enter the parcel's dimensions correctly. Of course, the problem with calculated postage is that you never know where your buyer will live so because I'm in Brisbane, I simply check the calculated postage to Perth which gives me the highest amount that would be payable, then I compare that with the cost of whichever satchel is most suitable for the item and list accordingly.

You can either add a $2 handling charge to cover eBay's FVF on postage, or if you're charging actual postage cost, you simply add $2 to the price of your item. If, as in your case, the buyer is in the same state, you simply refund the extra postage paid by putting the correct amount of cash in an envelope with the packing slip, so they don't mark you down on your postage DSRs.

Just last week I had 2 separate items which both weighed just over a kilo each but were wildly different sizes, but because of the bloody cubing rule, it was cheaper for me to send one in a 3kg satchel for $13.40 and the other in a 5kg satchel for $16.70. That's why I really hate dealing with anything which weighs more than 500g because regardless of size, a 500g (or less) parcel will go anywhere in Australia for just $7.20, which is crazy when you consider that a 500g satchel costs $8.25 yet its volume is comparatively tiny.