How should I deal with customers who are arguing about who gets to pay

I work alone as a cashier at a farmstand, and I never know how to react to people who argue over wanting to pay. Is there a way I can just make the whole interaction not awkward, I usually just stand there smiling. And every time it happens it goes on for a minute straight, and sometimes they make it seem like I'm the villain for choosing one side in the end. (for clarification, they argue about paying for the other person)