My best advice to avoid getting scammed is "if it seems too good to be true, it most definitely (not probably) is." I am also wary of bidding on private eBay auctions (how can you spot shill bidding that way?) and private feedback, or no feedback at all, stock photos instead of photos of the real item you're getting, among other things. Ebay's rules about authenticity turn replica sellers into liars. Replicas are illegal to sell anywhere. Yes, I own one (fairly nice ioffer fendi spy), but I am on an aspirational list at Neiman's for a real one. Sellers I've seen to be authentic on eBay are leshent and dudeiloveyou. I think there's a few others, like whitefashion and tedstar, but they're UK based and the exchange rate and shipper is a bit higher. Check their feedback and notice their items are usually going for more than retail value.
My advice if you want to get an authentic item is to suck it up, save up, and get on a waiting list at a boutique. If you can't wait, like me, get a fake from ioffer, where everyone seems to know what the name of the game is. It's still risky, though...
Okay, I ran the risk of getting scammed by wiring money Western Union to Guangzhou, China, ran the risk of having my fake bag confiscated by either Chinese or US customs, but that didn't happen. I would not have been surprised if it did. Strangely enough, the seller I bought my fake spy from (smartbag) is no longer an ioffer member and has loads of negative ratings from buyers. Now if they were "scammed" properly, that is, deliberately stolen from, I can't say. I think being a counterfeit bag maker/seller in China--or anywhere for that matter-- is a pretty dicey enterprise.
My main point is if losing $200 or so is a big hit for you, don't bid/offer, and if you want guaranteed authenticity, buy from the boutique or contact the boutique to find out who are authorized online retailers: eluxury, yoox, net-a-porter, Saks, and Neiman's are some that come to mind for many luxury brands.
I'm sorry to read of anyone getting scammed. I don't like that nasty "serves you right" attitude. Believe me, I dream of a $1000 truly authentic eBay cognac spy, but it ain't gonna happen. It's rice and beans until Christmas for me, and, hell, won't I be shabby chic with the real deal hanging off my arm. Hope all this helps someone...