charging your credit card without knowing up front

It sounds like you probably can dispute these charges. You might wish to report this to your state Attorney General and the Better Business Bureau (bbb.org). If the vendor cares about its reputation it will contact you to settle the dispute to clear its reputation with the BBB. Unfortunately many business don't take the BBB seriously but at least it may help others out who are careful enough to check with the BBB prior to purchase.

I am ALWAYS leery of any business that requires me to provide my credit card for any introductory service without purchase. A common "scam" (legitimate if proper disclosure is given but usually deceptive or misleading in practice) is the "autojoin" procedure, where if they don't hear from you after the introductory period.

Also make sure that on any site which you join that there is appropriate contact information such as address and especially telephone number. You may even wish to verify the number by calling prior to purchase unless the company name is a recognizeable brick and mortar.