You could try asking this question at the Chanel sub-forum, I´m sure they will now. Also, there is an authenticate this thread in which you can authenticate it with the Chanel-lovers before buying.
Yeah agree w/ nola & seahorseinstripes, post it to our chanel sub-forum for authenticity check. I think the boutique is no longer available for authenticity check, but you can always phone them and ask if they may. But first of all & most important thing is to check the seller's return & refund policies. Goodluck!