I've owned several properties in the City of Flint and have done real well over the years. As already mentioned, the location is key since the neighborhoods can change from bad to worse real quickly. As little as five years ago it was relatively easy to make a great profit with very little investment. Tenants were easy to come by and Flint didn't have as much of a negative connotation.
Notice the use of past tense.
That was then. I've sold all my Flint properties. The City has gone down hill quickly. Taxes are up. Water bills are outrageous. Crime is up. Blight is the new norm. Schools have declined. Finding tenants for these homes has become nearly impossible even for the most savvy investors.
Flint Township and the surrounding areas are a completely different story. The municipalities in Genesee County that border Oakland and Livingston are very affluent. In fact, finding properties in those communities under $100 a square foot is nearly impossible.
I'd be careful with Flint proper.