It's a game the scammers play. They know perfectly well that they've posted off dodgy crap, they just play games until the buyer gives up.
I've been caught four times (three sellers - inc one that changed his username and managed to get me twice). The three sellers had a few things in common:
1. Sell lots of stuff, usually mixed bag, low value stuff that's clearly not just cleaning out the shed;
2. Lots of bad feedback, although a lot if it is hidden as negative comments in "positive feedback". Always check the comments, not just the feedback percentage!
3. Any Negative feedback is met with denial/blame the buyer/blame AusPost. It's one thing to cop a dickhead buyer, but you know there's an issue when twenty people have complained, and the seller never once says "yep, sorry, sent the wrong thing" or "here's the tracking number" (etc), but ALWAYS says "was working perfectly when sent" or similar.
They're the three big warning signs. Also check for LOTS of positive feedback from the one buyer - it's clearly another account designed specifically to boost their positive:negative ratio.
They count on people saying "it's only $33, I can't be bothered". If you can't get a refund, then still make them work for their ill-gotten gains.