I get this question frequently enough I’m going to post this so I can have a convenient place to copy and paste from.
The credit card verification I use is pretty strict (as of November 2015 I haven’t EVER had a charge back or fraudulent transaction). Your billing address has to EXACTLY match what your credit card company has on file (if in doubt, pull up your card statement and see where they think you live). If it fails to verify you might still see an “Authorize” transaction on your card, this is from Stripe (the guys I use) saying
“hey dude, does this person have enough money to cover the charge? cool, by the way here is their address, does it match what you have? No? OK, never mind”.
If it does match then it does what’s termed a “Capture” transaction – this is where your card gets for realsies actually charged.
So the good news is: you don’t get charged for the AUTH transactions but they DO usually temporarily count towards your credit limit. After a few days, depending on the bank, the pending charges will drop off your account and all will be right with the world. Now if you need to you can usually call the bank and get them to release an AUTH early.