I accept that sellers have packaging costs and I accept that as a buyer we have to pay for these costs...

Yes I would know what I was paying upfront for if the buyer DID state on their listing that the postal cost was for postage and handling, as sellers should.

You make your own assumptions of implying that Im one of these so called people that make the assumption that they should have paid what was listed on the postage sticker.
In one of my posts I said that I would not dispute a few dollars difference in what I paid in postage to what showed on the label/sticker when i received the item..(even in the case of it not being listed that postage costs were for postage and handling)
The $30 and the $10 was just an example- but if I did pay $30 and found that the item cost $10 to send and there was no obvious reason for the large difference then yes I would query it...if you do not agree with that then thats fine by me.

My main grevience that I have brought up in posts was with the pre paid satchels, how they are probably used for convenience because the item would definitely fit in one no thought needed.. instead of seeing if it could fit in a smaller one or another form of cheaper packaging.