Beware of Credit Card Scams used in Fitness Gyms

I didn't cared much about this until later when I got my Credit card charged with un-Authorized transactions. To share this, I enrolled to a Fitness Gym. At first, I was hesitant to use my credit card but with good salestalk, I was blinded by the freebies provided for those who will register, and also avail their promo. Then, after I got everything OK, I was approached by one of their staff. I was told that there are other members who want to join, but don't have a credit card. So, this staff explained to me that they just need some credit card to be registered with their registration, so they can avail their promo but no charges will be sent to my credit card, as it will be nullified on purpose (Was explained to me that, they will just charge 1 peso and cancel the transaction, so no charges will be sent.). I'm just tired and really want to call it a day, so I said, OK but be sure that I won't have any trouble with this, which the staff expressively said "yes, absolutely no problem!".