Suppose in the near future you manage a pizza restaurant, and suppose a new electronic currency, Bitdollar, becomes popular. Your pizzas had been selling for $$12.$ If you accept Bitdollar for payment, you will incur a processing cost of $$1$ per transaction. You are considering raising the price of pizza for those who pay with Bitdollar to cover this additional expense. Research in Psychology and Behavioral Economics suggests that the way to increase prices to not appear unfair to customers is:

charge $$13$ for all pizza, no matter the method of payment

do not post the fee on the menu, but include the fee when giving customers the final bill

post menu prices as $$13$ for pizza, with a $$1$ discount for those who pay with cash, credit, or debit cards

post menu prices as $$12$ for pizza, with a $$1$ fee for those who pay with Bitdollar