If I buy book from an online shopping site via my credit card, how can the retailer get money from my credit card? What is in place to ensure the retailer gets the exact amount of money I should pay, no less no more? Is it a risk to tell someone my credit card number for them to be able to charge me, like when we fill in a credit card number in Amazon.com?
Thanks in advance!
When you give your credit card number and authorize a merchant to charge your credit card, the merchant then gives the information to their merchant processor which in turns bills the bank that issued the card (it's a little more complex and it all happens instantly unless the merchant is using the very old fasion imprinting gizmos).
It is possible for a merchant to attempt to charge you more than you authorized but if they do they risk a fine ($25-$50 for a chargeback) from their processor, the legitimate portion of the charge as well as increasing the processing fees charged by their processor or even the possibility of loosing their merchant account entirely and being permanently blacklisted by Visa/Mastercard. In short no legitimate business is going to intentionally over charge your credit card.
There really isn't significant risk in using a reputable online retailer's order forms. There is the possibility that their database could be compromised but that risk is lower than the risk of having an employee steal your credit number when you give it to them in person. Besides in the US at least the most you can legally be held liable for is $50 assuming you notice the discrepancy within 60 days of statement the charge appears on and most banks limit liability to $0.
Over the years I have had a number of different credit card numbers stolen and used fraudulently and I have never had to pay any fraudulent charges.
Your credit card limit is nothing more than a simple number. When you purchase something, the merchant receives a number (i.e. the amount of the transaction) from your card company (e.g. Visa) in their bank account, and that number is subtracted from your limit (added to your balance).
The amount is recorded, and isn't changed, so that's how they get the "exact" amount you paid. Transferring a number is easier than the retailer having to wait for cash to get from you to your card company to them. Moving numbers around is the basis of the modern financial system.
And yes, it is always a risk to let someone else have your credit card number. An untrustworthy company/person may use it to charge you without your permission, or if they have your full details they could use it as if they were you. With a reputable retailer like Amazon, the main risk is data theft: If a security hole is found in Amazon's system, someone could steal your credit card info and misuse it.
