Take 3 pairs, try them on then send 2 back at OO.com.au
And the best thing is that OO.com.au wear the cost of the return shipping or that is what they state in their email. BUT if you read the fine print in the terms and conditions they state this:
" Your refund will be the amount you paid for the items returned, net of a restocking fee of $7.95 per item returned." So a bit of contradiction there - might be best to ring them first.
Now just to clarify about the cashback for OO.com.au - you will ONLY receive cashback on the cost of the sunglasses you keep (minus GST of course), not the total of your order. And you may see a delay in the cashback appearing in your earnings