What is a surcharge?
A surcharge is an extra fee added to a credit card sale to cover the cost of taking the card. It applies to credit cards only, never debit.
Next: Washington surcharge rules · how dual pricing works · work out your processing fee
The card networks cap it and require you to register first, post a notice, and show the fee on its own line of the receipt. Washington allows it within those rules.
Not sure which one fits? See dual pricing vs cash discount vs surcharge side by side.
For example
A shop adds a 3% fee to a $100 credit card sale, so the customer pays $103. The same sale on a debit card gets no fee.