I've learned to always, ALWAYS ask when I first step into a cab whether they accept card payments, anywhere in the world. As far as I can remember, every time I've done this the answer has always been "yes" and the card payment worked without a hitch at the end of the ride. Yet just about every time I took a cab without asking about cards upfront, the driver would tell me his reader isn't working and he'd have to drive me to an ATM. Funny how conveniently finicky those readers are...

Counterexample -- happened near London. I asked to the cab driver if he accepted card payments and he says no. I asked him if we could stop to an ATM machine on the way and he said no and had me leave the cab (it was raining and there was a huge queue to get a cab).

Fair point -- if cabs are in high demand / short supply (and/or you're in a hurry) my strategy might not be ideal.

Many places (check in advance!) require the driver to be upfront if their card reader isn't working or you're not obligated to pay.

It's amazing how those finicky card readers miraculously start working when you say 'oh well, too bad I guess' and step out of the car!

That's a great strategy too if you know the law is on your side and are bold enough to pull it off. But I'm pretty non-confrontational (even when dealing with people I know are trying to cheat me) and when I take a cab I'm usually in an unfamiliar place where I didn't have the foresight to check on the cab regulations beforehand, so I'm going to stick with mine :)

In Berlin it's now illegal for them to transport passengers if their card reader is not operational.

Drivers have still pulled the ""my reader doesn't work" on friends.

I was half drunk / no sleep at the time. I probably did ask them, or just assumed like every other cab in the civilized world takes them. Anyhow, horrible.