NTAG4XX cards have a chip that prevents double billing and fraud with internal counter and extra parameters for every spend. True, we didn't use it Riga, but we can get this setup for future conferences... then the problem you mention will be solved.

I have also spoken with Vivek from Coinkite on getting SatsCards working with on BTCPay POS... can be done, just if enough time in the day can be found for coding...