I second the advice I just read, buy on eBay, you have eBay Buyer Protection, pay with Paypal and ONLY with a credit card, you have Paypal Buyer Protection (btw, you can CHOOSE whether to file a claim through eBay or Paypal when you do, both PREFER you use eBay Buyer Protection, but you can go through your Paypal Resolution Center, choose a transaction and directly file a claim there, but you can't file through both for the same transaction.) By using your Credit Card, you have the ultimate backup of being able to do a chargeback with your credit card issuer.
I have read here before of some people being unhappy because they bought LV that was used, got it in, took it to their local LV store and failed to get it authenticated and assumed it was not an original item, THAT IS NOT THE CASE by a long shot. Not even LV store managers are expert in authentication and that is especially true for older LV items. Secondly, it is in the store's financial interest for you NOT to buy used and to spend your money with them directly, thereby them getting the profit margin. I personally would not trust an LV store to authenticate any LV item for me.
Lastly, I have dealt with CarolDiva for years, never had any problem and trust her opinion over good good good, old old friends opinions anytime, anywhere, any place.
Bottom line, if you are not buying it brand new at an LV store, truth is, there is always some doubt, the only thing you can do is minimize it as much as possible.