@Chanel4Eva is talking about this program:
Shop designer handbags and accessories with confidence—just look for the checkmark.
pages.ebay.com
For the brands included in this program, I believe (but am not sure) that it covers any of the handbags over $500.
When the purchase is made, sellers ship to ebay where they have an unnamed team of experts who supposedly examine the bag and if confirmed as authentic, it's subsequently shipped to the buyer.
The problem is that no one knows who the "experts" are and ebay refuses to disclose.
There's a similar authenticity guaranteed program with sneakers and there have been many threads on ebay's discussion boards where mistakes have been made.
A huge problem is that if ebay's experts deem the item to be fake, the seller loses the item and the money. Not knowing how skilled the authenticators are, I think it's a scary thought to consider that authentic items can be mistakenly determined to be fake and the sellers lose.