is sexkey a safe verification mode?

Only if you want to know if he is over 18. Even for that it is not that useful since a lot of kids have their own credit cards.

They are using fake ads and real indy or agency information to get you to give your CC information out.
Under no circumstances should you be required to give out CC info just to get a reputable provider or agencies phone number or e-mail address.
We have been used as contact information for one of their scams and it's sad to see how many guys have given out their CC info just for a phone number or e-mail addy

Scott