A long time ago, Paypal used to offer one of the coolest possible features out there, the ability to create a debit card number that is either tied to a single vendor, or for use as a one-time transaction.
The obvious use for this was to protect your account from fraud if the site was ever compromised.
My preferred use for this was to create a merchant tied account that I could cancel once I decided that the business relationship was over. One of the really crappy things common today, when you try to end a business relationship, is when the vendor insists on playing games with you by continuing to charge your card or add some insane charge at the end that will require hours on the phone with them to resolve.
A common use for credit card number modulation is canceling your cable bill or other hard to cancel service. Instead of waiting on hold and then putting up with an annoying sales pitch. Call their retentions department, tell that person you are canceling your account and get their operator id number. Ask them where to return the equipment if needed. As soon as they start their retention bit, cancel the credit card. Once verified, nicely tell them that you have canceled the payment account and this conversation is over. Next, write up a simple document to the company's legal department with the operator's id number and contents of the conversation. If you are returning equipment, include a copy of this document taped to each piece of equipment. Also fax/mail a certified letter to the company's corporate number/address to the attention of the legal department.
Why should you go through this trouble? Because the company will slam you with fees and send you to collections since they can not charge it to your card. Direct TV tried this with me and this process with PayPal saved the day. 5 years later and I still get collections calls for my direct tv account that was canceled since I moved to a location that did not have a view of the southern sky. Each new collector gets a nastygram warning them to stop and that I will sue them if they continue. I also attach the cancelation fax, judgment letters and redacted check stubs from previous collection companies that I have sued in small claims court and won $500 - $2000 each time. It does not stop them, so it is a source of income every year or so.
My other use for credit card modulation is one time numbers. This is really handy for transactions where you do not trust the company for any length of time longer than this specific transaction. In my case, I use this for buying bitcoin and usenet feeds from international vendors.
This was all great until about three or four years ago when Paypal was forced to drop the service. MasterCard and Visa immediately added this service but either made it part of their premium card service or charged to have each number created.
In recent months, companies have started to address this gap. The one I am working with right now is Final Card. This is a credit card for good to excellent credit scores. Final Card focuses on credit card security. This is not a premium card so I am not sure if it is a good idea to rent a car on this. However, it is an excellent card for the use of its number modulation. Within minutes of approval, you will have access to their app and web page with the ability to generate card numbers. I quickly switched all of the accounts that I pay via my preferred Capital One Venture card, to their own specific vendor locked Final Card.
So far I am happy with the service. I will update this in the future.
If you are interested here is a link to the card. Final Card.