There are not many I would trust, but I have purchased from the following and they’ve been great service and the items have been 100% authentic

www.eluxury.com

www.Designeroutletboutique.com

www.zappos.com

www.bluefly.com

However my favorite from them all is www.Designeroutletboutique.com as they’re the cheapest and offer the ideal service.

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Answer:
I trust the official on the internet department stores (Neimans, Bloomies, Nordstrom, Saks, Barneys, etc.) and also the handbag maker's on the web stores.

Also: delfinoshop.com, bagshop.com and shopbop.com are trusted sites