Etsy hasn't announced anything as yet, AFAIK, but I will be very surprised if they don't follow suit with eBay.

No idea about the other site, though.

The GST won't be applicable to all sales from all international sites, though. If they are a standalone site, they're only required to collect it if their Aus turnover is $75k or more, and your purchase is under $1k. If it's over $1k, tax and duties will be payable the usual way.