Where do eBay sellers get their brand new textbooks?

I've been getting a lot of great deals on textbooks on ebay, usually in the international edition. It's the exact same textbook, except the cover is different. I just wonder where they get them, or how do they get the "connections" to sell them.Where do eBay sellers get their brand new textbooks?
You can get international versions of textbooks at most textbook websites. They are always cheaper and usually only have minor differences to the American versions. I use http://www.bigwords.com to compare textbook prices from all the online retailers and rental sites to make sure I'm getting the best prices.