If the seller has agreed to take off the postage costs there are two ways that they could do it, although which option he/she uses depends pretty much on whether you've already paid for the item.
If you haven't paid yet then the seller would need to send you an invoice. To do this the seller would need to pull up the drop-down list of options next to the item you've bought, then create an invoice for the item but adjust the postage costs accordingly. Once the seller has done that and has revised the postage costs to the amount that was agreed all he/she would need to do would be to send you the invoice and you could pay that way.
In the event that you have already paid for the item the seller would need to use a different method to take off the postage costs. In this instance the seller would need to log into his/her PayPal account and issue a partial refund for the amount that he/she agreed to reduce the price by. Once the seller had done that you would see the symbol next to the item in your Purchase History to indicate that the seller has issued a partial refund, and you would also be able to see evidence of the partial refund if you were to log into your PayPal account in order to check it there.
If your seller is still unsure as to how to resolve this problem by the time you read this response, then print this page off and copy type the instructions into an e-mail to the seller sent via eBay Messages, or if you don't have a printer then copy and paste the text from this message into your e-mail to the seller so that he/she can read the instructions and deal with the matter as appropriate.
