Ever been to a store where the clerk asks you if you'd wish to sign up for a store credit card? And, if you do so, you'll get 10% off today's purchase?
Tell them no to the credit card but that you'll take the 10% discount.
Ask to speak to a manager if they won't.
The in-store credit card is a gimmick to lure you into to buy more, to make more money by charging you a ridiculous interest rate on the credit card.
You'd be surprised at how many of the times they'll give it to you.
Because they have no reason not to.