I just completed repair of a violin with a crack in the top that went right through the purfling. Having the purfling there actually complicated the repair. I am not convinced purfling helps at all, since you have to weaken the plates by cutting a groove to install the purfling. However, there is the matter of TRADITION. Probably no violin (or cello) maker would dream of violating TRADITION. So, it is probably the case that painted purfling is a sign of an inferior factory built product. But just to be sure, look inside and out for signs of good vs. poor construction: rough surfaces, misaligned fingerboards, rough linings, visible glue lines, etc. Disclaimer: I am only an amateur repair person. Al