Couldn't agree more with Joe on this point.
We see a lot of people always chasing 'designer brands', but the simple truth is that all designers protect their brands by limiting their distribution into the marketplace which makes it impossible to get access to them if you're not linked up through their official distribution networks.
Maintaining this sort of market control is how they can maintain high prices on their brands and is what gives their brand name value.
If a designer just threw their door open to any wholesaler to distribute, the market would be saturated with their products, competition working as it does would see their prices reduced, and with that reduction in overall price comes a reduction in the brands name.
Closeout sales are one of the best sources I've seen for Designer Bags, and while the really top shelf names are hard to get, you can find them from time to time.
You will find closeout prices staying high on these types of products because of the demand from buyers, and 20% off retail at liquidation is pretty common, the good ones just don't get reduced much past that, and even then stock sells out rapidly.
If you really want to deal in a designer brand, then you really need to deal direct with the designers themselves and see if it's at all possible to gain access to their distribution network.
Hard task in itself, but I would say impossible without a bricks and mortar store.