EC is Eurocheque, a German specific card system. In my experience in Germany, lots of places take EC but neither visa, mastercard or amex, so in effect, only Germans can pay with credit in a lot of places. This is true even in Frankfurt (arguably the financial capital of Europe). In the cafeteria of a place I frequently work, they also don't take cash, so foreigners can't eat.

SEPA is the single euro payment area. Here it refers to the cost of a wire transfer.

Now that we are talking about card payments (NFC, chip and pin, etc.): jump into a random Frankfurt taxi in 2017, and IF they are willing to take your card (pretty big if), this will be their method of choice:

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They put your card in there, put a paper on top, and proceed to press and copy the embossing of all you card numbers into a carbon copy paper. Talk about swipe card insecurity... That is by far the slowest way, you spend 5 minutes easily.

I agree with the laundering / tax evasion cause only partly: I once wanted to pay upwards of 900€ in IKEA with mastercard. The cashier asked me to go to an ATM that was inside the IKEA building, take out cash from the card, and pay with that. With its scale, I don't think IKEA prefers cash to launder money or evade taxes...