I guess I have been fortunate. All the bottom brackets I have serviced have had cups that are in good shape. If the fixed cup refuses to budge I lay the frame down on the fixed cup and shine a bright light from the top looking at the bearing surface. Then I use my finger nail or a piece of plastic like a pen cap to gently feel the surface for any imperfections. In my experience the spindle seems to be the most vulnerable and that’s where I have had to use a bit of fine Emory cloth to smooth out, but only once or twice. Most of the time the assembly just needs cleaning and fresh grease. It makes it much easier when the fixed cup comes out but really not necessary. I have only had one or two I couldn’t get loose.