Designer Wedding Gown

how can websites afford to sell new Designer Wedding Gowns for so cheap?
Example- i love the designer Hollywood Dreams. However, the gowns are 3,000 +. Anyways, i found a few websites; namely helenebridal.com and ubrides.com that sell them all for 300. my question is how can they afford to do this? is it a scam? would i be wise not to order a dress online? have you?
it probably is a knock off. though theres nothing wrong with that, unless youre the designer of the gown. you can request a fabric sample on most sites that offer wedding gowns, but the only real difference is that the sewing quality might not be as good and the fabric might not be as luxurious. if they arent knock off then perhaps they are last years gowns, still new only not this seasons.
Wedding dresses – Pronovias NYC – Designer Bridal Runway Show 2011