The relevant law (art. 3 WZG[0]) requires persons to accept all banknotes (and up to 100 coins per transaction) as payment, but this only applies after a contract has been formed. It's perfectly legal for any store to indicate to customers that it will not accept large-denomination notes or cards[1]. If the customer is not willing or capable to pay using the accepted means of payment, no contract is formed, and the chewing gum remains with the store.
You say that, Espresso is a good source for this kind of thing and I'm not saying your wrong. But the letter of the law does state that everyone has to accept Swiss banknotes with no restrictions.
My personal legal asessment: If you were to form a contravt for purchase of goods and stipulated ahead of time that payment will be made in small bills (or electronic payments only), receiving payment with 1000.- bills would give the right to demand compensation related to handling large bills (security, verification etc.) due to the contractual breach, but it would not allow you to deny the money and demand payment as contracted.
The relevant law (art. 3 WZG[0]) requires persons to accept all banknotes (and up to 100 coins per transaction) as payment, but this only applies after a contract has been formed. It's perfectly legal for any store to indicate to customers that it will not accept large-denomination notes or cards[1]. If the customer is not willing or capable to pay using the accepted means of payment, no contract is formed, and the chewing gum remains with the store.
[0] https://www.admin.ch/opc/de/classified-compilation/19994336/...
[1] https://www.srf.ch/sendungen/kassensturz-espresso/geschaefte...