@Marcel Couch Classes for commercial properties are different than residential 1-4 family properties.
Also, you'll find the concept of classes for 1-4 family vary greatly as there's no standard and everyone has different opinions.
Our LOGICAL opinion is that it all revolves around the tenant pool for a property.
Here's our definitions of Class A-D, with the understanding that we are playing statistics and probabilities (there are always exceptions):
Class A: 680+ FICO, white-collar to high-blue collar, very stable career/income, usually some savings, takes very good care of rental property
Class B: 600-680 FICO, low white-collar to mid blue-collar, stable employment/income, often some savings, takes good care of rental property
Class C: 550-600 FICO, mid blue-collar to no-collar, decent stable employment/income, lives paycheck-to-paycheck, 50/50 on taking decent care of rental property or being hard on it.
Class D: <550 FICO, no-collar, unstable employment/income, often only SSI and/or Secion 8, often doesn't deal with banks, usually hard on a rental property.
The tenant class will eventually affect the property, which eventually affects the neighborhood class, which affects the contractor & PMC class willing to work there.
An abundance of housing will typically lead to a lowering of the overall class in that area.
A shortage of housing will lead to gentrification and improvement of overall class in that area. This is what many areas of the country are seeing currently.
Class A area values/rents are increasing, pricing out many and pushing them into Class B areas, which raises values/prices in those Class B areas, turing them eventually into Class A areas, but pushing people into Class C areas and so on.