The E bay B grades are generally not returns.
At the start of manufacture, if a cabinet comes from the 'paint shop' and has any imperfections at all, such as a tiny air bubble in the paint it is assigned a B Grade.
When you order, it is then built into a sub alongside all the others. Mine is a B grade but I'm damned if I can find the 'imperfection'. Their standards must be very high.
I highly recommend BK. I ordered a B Grade on the Friday and it arrived Wed morning looking brand new in every way.
Incidentally the XLS400FF is fantastic.