I had more than a couple out of 100 cells that were shown up by tinkling, though when I have had the occasional bad graft there have been higher incidences of this (a few times a season). I also cull cells that have the following attributes... short and stubby, very round blunt ends rather than tapered points, or excessively long (when compared to others from the same graft). my cells are generally very good and consistent so this doesn't usually result in a lot of discards either, except on the occasional bad graft take. I have found over time that these attributes are often indicators of cells that won't produce great virgins or queens. When you are rotating cells through mating nucs preventing dud cells going out is very important. Not only does it affect your percentages which in turn affect your ability to deliver on queens promised to clients it also means additional work as nucs miss a cycle of brood (from the newly mated queen) and can need additional boosting with brood or bees to maintain good strength for future cells.