Other PFers have already provided some great advice, here's my $0.02. There are a lot of honest sellers selling authentic items that are described accurately and honestly. And, there are a lot of dishonest sellers who use all kinds of tactics to make a quick buck. In order to tell the difference, educate yourself on the particular bag you want to buy - if possible, go see it in a store and really familiarize yourself with the details, and post a link to the website here in the appopriate authentication thread so other experts can help assess authenticity - AND educate yourself about eBay, including researching the seller's feedback/past items sold and familiarizing yourself with some of the cheap tricks dishonest sellers use. Finally, use common sense: for example, if you're after a super hot/just released bag that's selling at full price in stores, don't expect to get an authentic one on ebay at a discount.