Cellex-CAdvanced-C Serum, 1 Fl Oz (Pack of 1)

I just now spoke to Cellex C cust svc. dept. They say do not buy from Amazon it is not an authorized dealer. How can I be sure this is authentic?

How many people found it expired?

Is the bottle sealed and what is the expiration date on bottles sold now?

How long does the bottle last assuming 1 application per day?