Well, when are you going?
You could protect yourself by buying the ticket (verify with the seller that it's an old PH pass) a short time before you leave, pay extra for express mail, pay for the auction with Paypal and then go on your trip. Worse comes to worse you'd have to buy another 1 day ticket at full price, but if the ticket is bad, file a notice with paypal and get your money refunded within the time limit. You'd probably be out the postage, but hey, if it were someone who has a lot of good feedback I'd strongly consider it.