I recently joined this forum to help me (hopefully) gain information about Judith Leiber items. I am buying for my wife's collection and have seen this site mentioned often. I'll give you the benefit of my recent experiences on Ebay.
I have purchased over 250 JL items in the last 90 days, fully 80% of which came from Ebay. I read carefully, examine pics closely, use the "Ask a Question" link at the bottom of the ads and generally do all the things that any reasonable person would do in order to insure they know exactly what they're getting. I have never, not once, received an item that was not authentic (IMHO).
I have had sellers just throw the bag in to a box with some crumpeled paper and call it a day (i.e. they left the chain outside the bag). 2 difficult to find, pristine condition items were damaged this way. To their credit, both sellers offered to accept a return... but the items we're talking about here are things you don't see too often and, even damaged, at least my wife can say she has them. I now add a canned message to each payment informing the seller that if there is damage due to packing negligence I will expect a large credit refunded in compensation.
I am assuming that at least part of the audience here are actual collectors. I know a bit about collectors' mindsets from my extensive experience with antique firearms. Condition is everything in most cases. You take my rare egg bag and ding the side of it three or four times because you're an idiot and didn't pack the handle inside the bag... well, let's say that those folks missed out on a lot of potential future business.
Regardless, my experience in the last 90 days has been very good. I would say as long as you pay attention, ask plenty of questions and try to steer clear of sellers with few or no transactions, you should be fine.