There are some establishments, run both by expats and Ticos, who will charge a “gringo” price that is more than the normal price. But in my experience, this has been rare and has sometimes occurred when the merchant thinks I’m a tourist that they’ll never see again. Most merchants are good about charging fair prices to all who come in to their establishments. And once you become established in a community it will most likely not happen at all. In fact, once you are in a community and know people, you should start receiving “locals” discounts. Keep in mind that communities by the beach in tourist zones often have higher prices as a matter of course.
If you are traveling in Costa Rica and ever feel you’re getting the “gringo” price, don’t hesitate to walk away and patronize another place.