The lack of card should be reflected in the price, but lack of card doesn't ways equal not authentic. I have several Chanel's from my mum that don't have cards and my early Chanel's I didn't keep the cards for as it never crossed my mind at 21 that I may sell them! I also have some Hermes from my
Grandmother that I only know are real post having the, refurbished - the Constance is not even branded on the outside as, per Hermes in Paris, their bags that are 30odd years in age and older were not always branded, especially if they were special orders which was common at the time. Can you have it authentic fixated or looking at it, can you judge? Does the owner of the store have any background from the consigner? They can often tell from the other items from the same consigner over time if they think it is real or not..and they should be worried about their own reputation and not wanting to sell fakes..