95% of all designer brands ONLY sell their bags through authorized stores. Why do they do this? It allows them to control how the bags are advertised and how much they are advertised for. Brands have great value because of this control.

Take your major brands:
Coach - ONLY sold by COACH and approved MAJOR retailers.
LV - Only sold by LV and approved MAJOR retailers.
Gucci - Only Gucci and approved MAJOR retailers.

This is the same for most bags. The only other way that you can buy a real one of these bags would be from a business or website that has purchased from a retailer.

If you see a website online and it is full of LV bags and it is not the official LV site, do not waste your money.

If you see a single bag on Ebay, it may or may not be real. It is possible the bag you see was purchased from a retail store, possibly on sale or special, and is being re-sold.

I hope this helps, the internet is full of fakes.

Remember that it is not illegal for a company to copy a bag, but it is illegal to copy a logo. You can make a copy of a Coach bag as long as the Coach logo is not on it. Of course, who wants a Coach bag that doesn't say Coach on it. That is like putting on makeup to sit around the house.