there is a fairly extensive diverting network at work in the US - how else would retailers like Costco end up with brands like Samsonite, Lacoste, and RL? Some of the strategies that diverters have already been laid out in previous posts.
Basically, diverted inventory can come in several ways from what I understand. Sometimes for example, a store will go out of business, and a liquidator will sell off the inventory for said retailer. Other times, a store will be affected by a hurricane or flood - and the merchandise liquidated by an insurance company.
Other times, diverters can persuade shop owners to abuse their wholesale account privilegs (i.e. buy me 20 RLPL sweatshirts from RL, I'll pay you in cash for cost + 10%, on the spot.
And of course, factory over runs or product for cancelled orders is indeed out there and can be had if you know how to use the network.
At any rate, these strategies can assist in getting cheap luxury goods onto the ebay marketplace.