I think it's a lot more effort to make fake bags than to make a fake receipt and there are plenty of people making counterfeit bags. People even take real authenticity tags of authentic wallets (e.g. Bottega Veneta) and sewn to fake tote bags!
How could I know if this particular seller is reputable or not? There are plenty of 100% feedback sellers that sell fake. I am a 100% feedback seller myself and I encourage any of my potential buyers to seek opinions before entering any transactions. I don't get offended at all. Not a bit.
Did I break any rules for using this free service that some experts are kindly providing?
Absolutely not. You were in the right.
