To me A grade means ease of leasing and management. Its easy to lease to someone with a good job and plus 700 credit. As a result collecting rent is fairly easy. Afterward things like maintenance the tenant will accommodate you on like be dependable to coordinate a repair and be home to let them in. B grade you can get the same tenant but have to work harder to find them when leasing. C grade you can't get that tenant anymore and are in a higher risk status as a result. Many will still pay but get ready to have that bad feeling around this time of the month as the tenants are late. Occasionally they are really late and eventually it will effect your vacancy. D grade and your dealing with evictions and higher vacancy because no one who can live somewhere else will live there.
In Baltimore there is a lot of dishonest turnkey providers selling stuff in the 200k range that seems somewhat close to the inner harbor. A lot of it is really bad but there is some stuff close by there but on the good side or the 83 corridor that is in an A area that makes sense right around 200k. I would get a local agent that knows the neighborhoods. If you physically go there especially at night it should be more obvious. But there are some gray areas. I'm a local agent and can help with that if you want to shoot me a pm.
One thing I would do if I were starting in a new city to verify whether a neighborhood is good is look at the BP blogs here. I would also consider calling a larger reputable pm company with a good Google rating about where they manage and recommend buying property. A good pm will not manage in rough neighborhoods bc its waiting their time and not profitable not to mention risky. Thus they should give a good indicator about where to invest. A lot of them will be helpful for you towards this for a few minutes discussion.