I've bought tickets advertised on here (at not much over face value). I've got them for free from people who had spare corporate giveaways (and I've been on the other end and given away spare corporate tickets, particularly for Friday & Saturday - no I don't have any this year so please don't ask!). And I've bought them from guys in the streets up from CWB MTR to the ground - again for not that much above face value (say$500 for a Saturday ticket).
This year Mrs PDLM is playing netball for a rugby club's team so we get two guaranteed tickets that way
