Over the past 6-7 years, I have purchased probably 50 one-time passes off eBay. I've only been burned once (this year) in a very similar fashion to RoseB above; the seller was mortified and claimed the card was still active, and I also got a prompt refund. Buying passes off eBay always carries risk, but I'm comfortable with it. Two tips I would offer are to purchase one-time passes only within a few days of travel and never pay more than $30 for one pass.