At the end of the day, authenticating is an inexact science at best. Human beings are working off of photographs that aren't always optimal to do the job. The only real assurance anyone can get that they have an authentic designer items is to pony up the cash and buy it at the designer's boutique. Anyone looking for a bargain is looking for trouble. Period.
Very true regarding it being an inexact science.
However, even purchasing at the boutique isn't always a guarantee of authenticity. My BFF buys lots of LVs, and she was looking to purchase several from a woman who had bought all of her bags at an LV boutique around here. When my BFF looked at it closely, it turned out that the bags were superfakes. She told the lady about it and figured she was just trying to pass of fakes as authentic bags. But the lady was livid and went back to the boutique where she bought all the bags, Turns out, her SA there had been selling her fake bags for years and she had no idea. I know the SA didn't work there anymore, and I don't know if he got fired because LV found out or they found out after the fact, but I know the boutique was seeking legal action against him. And this was an SA she worked with for a long time.

I mean, that's the only time that I've ever heard of that happening to someone I know, but that's just crazy. I really thought the lady was just a scammer and she would disappear once my BFF told her the bag was fake, but my BFF was in contact with LV regarding the issue (since she was helping the lady to let her know which ones were fake), so I don't think the story was BS. Super scary though.