From our prospective, Granada is very safe! However, we do have pick pockets and tourists forget a few basics. Never leave purse or back pack on the table, place on floor under the table. In reference to cars, never ever leave stuff in plain sight. And never pack the car when you exit to shop or walk around. Have all goods in trunk prior to exiting the car.
Last week we saw a family with 3 kids from Phoenix at a local restaurant. I noticed them walking back and forth an pulling stuff out of car and going back to restaurant. I went to the car an noticed a back pack and electronics in clear site. I went back in and informed the couple that they need to be very careful or otherwise they would have a negative experience in Nicaragua. Would they do this back home? Most likely not so don't do this in Nicaragua.
In bars do not flash money. Best to leave to bar with a minimum amount of funds. A trick I always do, I place extra funds in my socks. Do not go bar hopping with your drivers license on you or passport. A family friend got pick pocketed for flashing monies and the ladies targeted him with drinks. A few hours later no money, no phone and no ID. He later agreed, it was his mistake to flash monies around and assuming all people in the bar where there to have a good time!
The negative experience occurs because some tourists do not take precautions! Please be careful and you will have a wonderful experience in Nicaragua.