Hi Ali, I know shop owners but Im not sure if they would provide more insights themselves. I will try asking them next time.
Nonetheless I personally gained informations / insights usually after facing hurdles or rejections using my cards to shop there and asking the owner.
Im talking about shops with relativ high customer frequency and low to medium bills per customer.
A bakery, butcher, snack shop, Cafe with 3-6 Euro bill per customer would suffer from high fixed fee per transactions. 15 euro cent fixed fee per transaction plus scheme disagio can easily result in 5-6 % on a 5 Euro bill. They told me thats to expensive, they cannot afford to spend so much money on payments so they use either high minimum purchase hurdles for debit- and credit cards, accept only cash or only ELV (german direct debit) which is clearly outdated.
The 2nd concern is speed of card payment. Thats no problem at a supermarket with a powerful but expensive computerised cash register + Igenico pin maschine. Cheaper mobile solution (iZettle / sumup) might not work as fast and doesn't easily connect with the current cash register. That extends into book keeping. iZettle und sumup payout are net (after fees) per bill. Example a 5 Euro bill would be a payout of 4,95 which make book keeping confusing with 100-200 bills a month.
The final concern is the time till the money paid by card arrives at the owners business account. I heard of example of many days... up to a week. One owner told me he cannot afford to wait 3-5 days to get access to the money (arriving account) cause he need to work with the money, purchasing goods to restock the shop.
Pinnen is so common in NL, not in Germany. It started to pick up recently but mostly at larger chain stores. No or even false knowledge about card payment solution is typical as well. The market of payment service providers is not transparent. Except sump and iZettle full card payment pricing schedules are not available , complicated / hidden or only shown if you request an offer for a payment solution. All that feeds the false assumptions and reluctance of german shop owners to offer card payments.