Mia,
My wife and I live in one of these "sketchy" neighborhoods you're talking about (Grant Hills) and I would just say don't judge a book by its cover. People that have lived in San Diego a long time know how bad these areas were compared to what they are now and unfortunately they carry a bad reputation because of that. I won't pretend like its the best neighborhood in San Diego, but it has good and bad parts as to be expected.
Some mentioned it already, but its just a working class neighborhood with good people. If you check out crime statics for the area, the crime rate is actually higher in "fancy" areas like North Park than in some of the "sketchy" neighborhoods.
If you're planning on living in the property I would say the most important thing is to spend some time in the neighborhood at different times throughout the day/week in order for you to feel comfortable where you will live. If you want to know more send me a message and we can talk about the area.