The CC on the front looks off-center. It's crooked and also not centered on the quilt. It should have a picture of a hologram sticker or serial number, if this isn't already in your possession then I would ask the person selling it for that picture, and if you currently have it and you can't find that then I would say this purse is not authentic.
Is this the same bag as the one you're looking at?:
CHANEL Women - Handbags - Medium leather bag CHANEL on YOOX