Beware of false guides
There are some young boys displaced in motorbikes that approach tourists offering services as guide. Always demand the presentation of the official guide’s card.
I had none of the related bad experiences, but the guy that led me to the hotel and wanted to lead me in the Medina the next day didn’t come because… he was arrested during the night.
The hotel booked me an official guide, and we felt absolutely safe with him.
The narrow streets in the Medina are tricky for a tourist.
Hidden by the displayed paraphernalia and the moving crowds, some jewels of the city’s history may pass unnoticed without a warning. I think that no tourist risks too enter without a local guide, so the risk is minimum, but if you are in a big group, even a small distance to the guide may betray you.