I know where. Often companies toss the merchandise that aren't moving into a dumpster out back. Along comes an enterprising fellow sometime around 2 A.M. and does some dumpster diving. A few days later, that merchandise shows up on eBay.
Bless that enterprising fellah! Dumpster diving is not for moi. I won my new Qi gong tape for $11 delivered, would have paid more than $35 for it at amazon.com plus tax and shipping. I read sellers' feedback reports carefully. Without extra good ratings, I'd never risk a dime.