You can have 100,000 Euros cash. You can’t buy anything that costs more than 1000 Euros unless you pay for it with a bank card. That won’t affect private sales much but if you go to a store and want to buy a new refrigerator and it costs over 1000 Euros they will ask you for a card. If you want to buy 3 separate items for 999 Euros each and pay cash then that’s no problem.
It's ridiculous anyone would make a law like that.