Credit cards are perhaps the most egregious example of them all.
A credit card is a paper wallet which may contain one single address. The address is composed of 16 numeric digits, which are usually formatted with three dashes, and it is secured by a "secret" private key which is... four digits long. To further securitize this secure security, a three digit super-key is printed on the back of the paper wallet in question, and that's it, you're good to go!
How is this abomination to be used in practice ?
Oh, that's simple - just like its users. For instance you can walk up to a machine, stick your paper wallet into it, and then type the private key. Yeah, that's right, you type your private key into a big box you don't own, nor control in any way, and can't inspect. What protects you from the owner of the machine selectively scamming ?
A shoddy, slow, bug ridden, unauditable, ad-hoc reimplementation of the common WoT.
And if the operator decides to charge your card twice, or fifty billiard times, the best you can do is call an Indian. They'll be thrilled to listen and eagerly try to help! Have you tried rebooting your credit card wallet sir ?
From: The Thoughts of Chairman Mircea.
The special streamlined identity verification process for Credit Card Altcoin businesses