No need to ask. Just inform to pay using CC.

Here's the typical scenario:
Me : Pay by card yaaa...
Cashier: Amount is RMxx.xx. ... (Waiting...) (Waiting...) (Waiting...)... Sir, may I have ur CC.
Me : Errmmm, I'm paying using Sammy Pay....
Cashier: Sorry sir, we don't accept Sammy Pay service....Only physical CC...We hv old terminal...
Me: Don't worry, just treat it like ordinary CC payment. Do the same steps in that terminal....Can...?
Cashier: OK.. let's try... (Face really kan-chiong...LOL...)
Me : (Tap the terminal...Sammy pay acknowledged check-mark....Meaning it goes thru successfully...)
Cashier: O-M-G!!!... I didn't know it works with this old terminal...
Me: So, next customer pay using Sammy Pay, u know what to do yaa....

It's very sad many merchants don't know the existence of Sammy Pay service. They worry we hack their CC terminal...LOL...