Some Grids have the ability to project some values with default constants per column. For example show 1 as true, 0 as false, NULL as N/A, etc. Please consult the help for the grid control you are using.
You also could opt for your own type converters. LLBLGen comes with a StringBoolean typeConverter. Please read more about this on the documentation. As for N/A I'm not sure if a typeconverter should be wise to use, as N/A is more a GUI representation problem.