I am a regular attendee of the answer boards and time and again the following statement is made by ebayers
"...how can this sellar charge £5.00 (example) for this item yet when I received the item the postage stamp clearly stated that the post only cost £3.50 (example) - I am a fairly new sellar although I have been a buyer for a quite some time - here is my response to this continually raised matter:-
At the time you bid on the item you are aware of the postage costs as they should be listed - if they were not listed then you should not bid before checking this out with the sellar - if you feel the postage is too high then DO NOT BID - nobody is forcing you to bid after all - if you bid and win and then decide that the postage is too high then you will still be expected to pay the amount listed or the sellar will basically report you as a non-payer which will leave you with a strike against you...not what you need for the sake of taking a few precautions before you bid.
Sellers are allowed to list "all reasonable costs" to the postal costs - this would include the packaging, whether it be bubble wrap, envelope, box, secure bag, sellotape - the petrol cost of going to the post office etc - so you will rarely have to only pay the cost of the stamp - and obviously always remember the extra cost of sending recorded etc would be included in the postal cost.
I agree that some sellers on ebay do overdo the "all reasonable costs" part and list an item with a £10 postage cost when the item is obviously not going to come anywhere near that amount - use your own initiative and do not bid on these items if you disagree with the amount as I agree these sellers are merely covering the fact that they will sell their item for a bargain price as the postal charge will more than make up for it.......
I hope this advice will be of help to you!