To Buy or Not to Buy?

So here's the deal.  You already know that I found THE dress: Alfred Angelo Style 217 (the premium Belle dress).   When I tried the dress on in the store it had a zipper back, so I didn't even consider any other option.  However, I found THE dress, new with tags and in the bag, on sale on preownedweddingdresses.com for exactly half of the price of buying it in store.  I can get the dress for only $800!!  The only problem is that it has a corset back instead of the zipper and I don't know how I feel about it.  Time to make a decision....any thoughts?