I've seen a case where this seller is offering a receipt for repair in the auction to bait bidders. The bag itself, well... FAKE!
She has this sob story where when she purchase the bag, the lock/key was broken so she took it to Hermes to get it fixed. Hermes would never accept a bag if it's fake, right? So, she use this as her weapon to convince bidders that her bag is real. For all we know, it could be another bag that's been repaired, and not that the one in auction.
I rarely buy a bag that comes with a receipt, but they have been fine.So, receipt is not the key, knowing the stuff is the key imo.