This advice from the Gringo Gazette, November 18, 2013:
Police Step Up Shake Downs
Police from La Paz to Cabo, and especially including Todos Santos have recently stepped up their efforts to shake down foreigners for money.
People, do not feed them, you only make it worse for yourself and everyone else. If nobody gave them cash they would stop asking.
When you are stopped, and you have made a boo boo, ask for a ticket and go down to the police station later on or the next day or the next week and pay it. They will take your driver’s license to insure you show up, and that’s ok. They do not want your license, as there is nothing they can do with it. Give it to them. You will get it back.
If you have not pulled a bone head traffic infraction, just keep asking for a ticket. “Dar me un ticket, por favor”, if you want to be polite. Be polite but firm. If they threaten you or get nasty, (the police in Todos Santos are saying they will pick up the money later in the foreigners’ home and ask for your address, which is clearly calculated to frighten), write down their name, or if they are not wearing their name badge, (mandatory, but still they often don’t wear it when they are up to no good), then haul out your phone and take their picture. That’s like holding a mirror up to a vampire and they will jump in their car and scurry away like cockroaches. Guarantee, they will let you go with some face saving mumble like, “just a warning this time”.
They rarely write tickets, and for sure they will not cite you when you haven’t done anything wrong. If you have broken the law, the ticket is ridiculously small. Man up and go down and pay it.
OK, once more now, altogether, “dar may un teeket”.
This police extortion would stop in a week if everyone would grow a back bone and stand up to them.