Hi @KevinSAFG! There's not a way to set a preferred payment method for a customer, though that would be very handy to have.
One workaround I can think of is to create a custom field called "Preferred Payment Method" or something and then write in the customer's preference. The main downside (if you're using the Square app on your phone/tablet at least) is that the custom field wouldn't be visible on the checkout screen so you'd have to check their profile before you charge them.
You can find the steps to create a custom field here.
