My advice to you is don't do it.
I often cancelled buy attempts and abandoned the sites when I got asked for my credit card number right in the face.
Often, the site is so poorly designed with no answers to obvious questions that you have to go through the complete form hoping to find answer in the process. Do they offer this particular shipment option? How much does this cost? Do they send to a package station or only to my home address? Do they provide an extra line for an address for me to use the "c/o" technique? I often could not find answers to these question anywhere on the site. So I either found them in the form before entering my payment details, in very few cases I did call them, in most others I just chose other places to buy from.
One more use case. In many places I've seen they only show you if they have an item on stock on the very last page of the order form. Not many people would want to "commit" to the payment right away without getting all the required information. You enter your credit card number, then on the second page you see they don't offer the shipment option you need, on the last page it says "the item is currently out of stock - delivery awaited in 3-4 weeks". And the order is already placed. Then it is a commitment from the user but not from the company, many will react emotionally to this approach as to scam and request their money back immediately.
The important thing is to behave friendly to your customers, don't scare them away, don't raise suspicions in them, don't make them regret they committed to their buying. Make them feel relaxed and happy and never with their arms bound.