I returned from Acapulco early June. We were twice victims of a police shakedown -- 10 minutes apart.
We were driving a rental car on the downtown strip at noon, and a "tourist" officer on foot signaled a police car to pull us over. We were just driving in a traffic jam with all other cars going 10 mph. He demanded money from us. We insisted to go the police station or for him to give us a ticket but he won't give the license back -- he got his $20 after ten minutes of debate. At some point, we just wanted to get out of there and gave in to corruption.
Ten minutes later, a "city" police car pulled us over an attempted the same. Out of money, we were much more aggressive -- and he let us go within 2 minutes.
When I called the tourist police office to report it with the help of resort staff, they asked for us to come in person to make a report. I laughed, since BOTH incidents happend less than 1 mile from the office!! I wasn't leaving the resort until it was time to get to the airport.
I reached out to the US Consulate, who of course is all too familiar with this story. His advice is to basically keep insisting on a ticket or to go to police station -- which we attempted. Try to get as much information on the police as you can and the consular will help report the incident. I also learned from staff at the resort that the police cannot issue tickets to tourists as an attempt to stop this police behavior -- clearly it didn't work.
After sharing this story, two friends had worse first hand experiences in Acapulco. We are grateful to be phyically unharmed. My family will never go back to any part of Mexico.
If you do decide to go, make sure you have the US Consular's phone number in your cell phone.