On the other hand, I could vouch for a complete different experience... in Moscow. I enrolled in a free tour, the ones that are willing to accept tips at the end, and it was fun all the way. It really depends on the guide.

The lady on my Moscow 2-hour tour was absolutely against Putin, claiming that after comunism now they were under a Putinism but the democracy was still to be experienced, etc etc; Lots of political jokes about the soviet era and the current environment... overall she was really funny.

Regardless, I consider Saint Petersburg a walking city, monuments close by and a city where riding the subway and sight-seeing their magnificent stations an experience to be had, thus a guide is not really necessary, similar to other cities in Europe.

Apparently the OP has already given the guide his business, thus now he has to hope that the assigned person will be a great fun guide.

PS - I appreciate the uncertainty felt by the OP; I was in his shoes myself, my own concern on not finding anyone/anything written in English. In the end, nothing to worry about. If one has survived Bangkok, one will surely survive Russia and after a few days I was learning, by my own, their Cyrillic alphabet. Easy !