I can't comment on this particular reseller, but in general:
1. I would always get a separate authentication from BB prior to purchase, regardless of what the reseller says about the item's authenticity (unless they already can furnish it for you (and even then, if I didn't know them, would verify)
2. If there is any issue with them providing the correct photos, saying it's not needed, etc., that's a large red flag. I have dealt with resellers who have offered to deduct BB's fee, should I buy the bag in question- that's a standard I would look for. ( Just because they are that positive of its authenticity, did NOT stop me from getting BB's opinion, BTW)
3. I would never send money ( wire, CC etc.) as a down payment contingent upon an authentication etc.- but that's me.
4. I have sent photos etc. to BB for authentication and just waited until I hear ( usually her turn around time is excellent), and only then seriously considered purchase. If it's gone, so be it. What I have found is, with H, there's always another wonderful bag waiting.
Hope this helps!