From my own experience working on retail/hospitality the main differences come with using swiping machines from different banks. And the main reason why they work poorly is almost always due to the GPRS signal being bad. Some of them also have a tendency of freezing/turning off suddenly… It is quite easy for instance on a busy shift in a bar or restaurant to knock them and for then to fall to the floor, so this might contribute to them not working all that well
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