There's no point being offended by eBay's fee structure, on moral or ethical grounds - as in, this won't fly with the ACCC. It didn't several years ago, and it definitely won't now.
If you want to make a change, you would need solid evidence of that fee structure being in breach of specific laws / regulations, or you will need to prove that it actively stifles competition and / or hurts consumer choice (and those aren't points you can work backwards on, or find a theory that matches and conclude it must be true, you need data that proves it. Being personally disadvantaged by it also won't matter to the ACCC, because in a nutshell all you would be saying to them is "I contracted a service and then when I was made to pay for it, I thought it was too expensive, despite it being the exact percentage of X I knew it was going to be").
There are many practices eBay should be taken to task for, IMHO, I laid quite a few of them out in the survey the ACCC recently conducted, but JMHO the fees on postage is one of the more benign ones. That survey is now closed, but you can find more info about it here - it's worth taking a look at, because it will help show you exactly what the ACCC is interested in when looking at online marketplaces. (My impression was that they were most interested in the "other" site's practices, the one where they have their own warehouse and often sell the same things their sellers do, and just threw a couple of other sites into the mix in the interest of looking fair / unbiased, lol). https://consultation.accc.gov.au/mergers-and-adjudication/survey-for-small-business-sellers-general-...
