When GST was implemented in 2000, retailers were prosecuted if they
1. Didn't state the GST inclusive price
2. Tried to markup items beyond the 10%

eBay, as a retailer, should be prosecuted as they
1. Don't provide the GST inclusive prices
2. Embed the GST in a whole lot of unrelated charges.

I don't use eBay to transact with the US or UK anymore, I liase directly as eBay is deceptively taking us to the cleaners