My paranoia aside, here's two pairs of Crocs shoes of size 6 and 8 which I've bought online (who can resist cheap deals? I can't).
They look pretty authentic:
I'm a size 8 and I find that it fits me well, but my mum who is a size 6 find it too tight. So here's a suggestion: visit your nearest Crocs outlet and try the size first before buying online!
Source: Gmarket
Rating: 9/10
Price: $8.90 each + Free shipping