I've read too many horror stories about E-Bay and don't visit it. I've only used Amazon twice and they haven't disappointed me.
I've had over 100 purchases on eBay, never burned once. They have ratings systems to avoid this... only buy from a seller with very high feedback or a minimum of a few thousand transactions and you'll be sound as a pound.
I picked up Enterprise season 4 at my local used media shop... for $20. It was a real steal ,even in CAD!