Some tourist shops and large supermarkets will take your dollars and give you change in pesos. Again, be observan and careful when doing so. Credit cards are useful in large centers and are essential when renting a car. Gas stations only take pesos . Businesses may add a surcharge for credit card use.
Cash advances are available at banks.
When looking to buy that Mexican Hat or trinket at a market or on the beach you will have your fun bargaining there. Most of the vendors will speak English and will enjoy talking with you in a conversation as best they can with most pretty adept to the language. To do better in pricing, insist on price bargaining in pesos. If you're not interested, just say so discretely and politely and most venders won't bother you. However, If you are interested, you should know your prices by having shopped in the stores.