You are perfectly entitled to your opinion and how you choose to work or not work with a business. But from the reseller's perspective, they sold you an authentic bag, with an authentication certificate, more than 3 years ago. To be then contacted by you after 3 years and to be accused of selling a fake bag by you, if I was the reseller, I would have thought it was ridiculous and be defensive about it! You labelled them an "amateur seller" on a public forum despite the fact that you said you had worked with them previously in selling and it went fine. So like I said, you do whatever you feel comfortable with but I have seen no evidence what the seller did wrong.
I am out!
Agree. 100%. And JMHO that it was unnecessary to make this long drawn out post without authenticating it first. To trash this company in the manner you described everywhere you can is overreaching. This is someone's livelihood. I hope you also reported how satisfied you had been with them for many years and that the bag was in fact authentic and you failed to get it authenticated before you started making claims.