Ebay is flooded with fake MJ bags, it's really bad for both buyers and sellers nowadays. I bought 4 discontinued/older MJ bags from ebay before, two of them were from familar & trustworthy sellers. I'm still very nervous about good-fakes, having the correct hardware details is not good enough for me. For color combination that I'm not familiar with, I have to check with friends who followed MJ from way back. I seek advises from friends on sellers' previously sold items as well -- to be absolutely sure. It was just too stressful (not worth it) for me, I just browse for fun now.
I am lucky to live in a city with many shopping centers. Unless the seller is totally trustworthy & reliable (only some that I would buy from), I won't take the ebay route no matter how good the deal is. I just don't buy it if I don't want to pay enough $$ for it.
A bag's authenticity can only be guaranteed if and only if it was purchased from an authorized retailer of a particular brand (boutiques,
Nordstrom, Bergdorf Goodman, Neiman Marcus, Barney's, Bloomingdale's, Saks, Eluxury, NAP, etc). Buying designer handbags from retail partners is the safest bet.
I no longer authenticate bags, I am officially retired from MJ authentication.