We stayed in Petersburg for several nights at the Waterfront. The place is very close to the ferry terminal so you do not have to carry your luggage far. Our room was comfortable but clean. Our host appeared to be initially sort of standoffish but once you got to know him, he was quite friendly.
Breakfast choices were limited but tasted good. He also said that if we wanted to use the kitchen facilities to make our dinner, it was OK as long as we cleaned up afterward. You can't ask for more than that.
There is really not a lot to do in Petersburg and we stayed there mainly because of ferry schedules. The Waterfront B&B was an acceptable place to stay for a few days.