I understand that ebay includes postage when calculating their fee. I'm not complaining about ebay's fees.

Here's an example to illustrate the point I'm making. Let's say I'm selling something like a concert ticket. It has a face value of $50 and I'm happy to sell it for its face value. The buyer is happy to pay the face value. I'm also happy to pay ebay's fees for the convenience of them finding me a buyer and handling the transaction. If the buyer is in Australia and is happy for me to post the ticket in the mail with a standard $1.10 stamp, my ebay fee will be $7.15, ie 14% of the face value of the ticket. I would consider that to be a reasonable fee for the convenience ebay provides me with. If the buyer asks me to send it by Express Post at a cost to them of $7.45, my ebay fee will be $8.00, ie 16% of the face value of the ticket. Probably still not unreasonable. However, if they ask me to courier across the country it at a cost to them of $70, then my ebay fees will be $16.38, ie 33% of the face value of the ticket. That's no longer reasonable, but if the buyer requests it, I'm kind of stuck with it. If they're in another country and want it couriered as fast as possible at a cost to them of $200, my ebay fee will be $36.55, ie I will have paid ebay fees of 73% of face value of the ticket.

So in this example, whether I pay 14% or 73% of the indisputable value of the ticket in ebay fees is determined by where the buyer is and how they choose to have it sent to them. I could refuse to courier it, but that could lead to a dispute. I could charge the buyer for the extra ebay fees I will incur because of their choice of shipping method. So for example, if the buyer is overseas and is happy with economy air at a cost to them of $3.40, I will end up with $41.96. If they wanted it couriered and I still wanted to end up with $41.96, I'd need to charge them $233.35 for the $200 courier and keep the extra $33.35. That gets complicated because every extra cent you charge them for postage increases the ebay fees. But if I don't do something like that, I'm going to end up with $13.45 from my $50 ticket, instead of $41.96, because of something the buyer decided to do that's of no benefit to me.