This sounds like good advice. I have not been on this cruise but a good friend went on it with her husband two years ago. They only used the shore excursions sold on board. She mentioned that they were warned to beware of pickpockets, especially groups of small children who distract you.

You may also want to check out any websites that your government puts up showing warnings about various destinations. Our Foreign Affairs (Canada) site at this time specifically mentions criminals pretending to be police offcers in St. Petersburg. Being escorted by a ship-sanctioned tour guide would give me a better feeling of safety.