Easy..
for me when I'm buying stuff, I let them scan the price tag first
without asking Samsung Pay accepted or not,
After scan every thing and come out the total bill,
then I only say use Samsung Pay.
if they refused to try Samsung Pay, then I say I didn't bring cash & card.
Tell the cashier either u try Samsung Pay, or I don't want to buy d.
In scenario like this they will need to call their supervisor come in order to cancel items that have been scanned,
and they need to arrange back the items that I took,
end end they spent effort but didn't get any sales.
The cashier wanna give me trouble, I give them trouble back.
They also can't penalize me because I'm not stealing, and I got money to pay and really wanna buy things, but they don't want accept my payment method only.
Or else, ask them put signboard big big at entrance say "No Samsung Pay Allowed" , just like some shop indicate "Cash Only" .
Then let see what Samsung / Mastercard / bank will do to them.
Every Samsung Pay user harus bersatu, use the above method,
if only me alone doing so, the force is not big enough,
If every do so as above, we definitely can bring a great impact to all the mechants.
And above method also didn't violate any Malaysia Law, so no need scare of doing so.
Maybe try not to tell them you want to pay by "Samsung Pay" just tell them I want to pay by "Pay Wave" when they set everything ready then only flag out the phone and tap on it, they got nothing to say by then