Like Walter says, it's hard to say with a helmet as there are some ways to buck the system. Few do, but it does happen.
There are literally hundreds of helmets that come through tech and make it to the track, and we try to - and are usually quite successful at - inspecting all of them. Sometimes a helmet that has superficial and cosmetic damage will be allowed a tech sticker. This is almost always limited to paint only issues with no visible and significant structural damage (meaning appreciable gouging into the shell or cracks). These cases are not common, and we reject quite a few that helmet owners claim to be okay since safety is the priority. In those cases where we do allow a pass for cosmetic issues, we usually recommend that a new helmet be procured soon anyway as it is literally impossible to tell if a helmet's crush liner has absorbed impact and deformed even if the outer shell doesn't appear to damaged (this is often the case paint scuffs from crashes that happen off the pavement, such as sliding in the grass - the helmet may not look bad, but who knows on the inside?).
I don't tech every helmet, but generally speaking if a helmet is a judgement call, the other tech officials will defer to me when I am in the tech barn, and I refuse more than I pass.