Diseases that can be transmitted up via the egg are pretty rare but it could happen....being NPIP certiied doesn't test for those diseases. And being NPIP certified only tells someone that the flock (actually a small percentage of the flock is tested) was 'free of disease' at the time of testing.
I have bought eggs on eBay many times, never have had disease's from those eggs, some were NPIP, some not....actually it's safer than buying juvenile or full grown birds from a breeder, especially the ones who advertise on Craigslist.
I have bought eggs on eBay many times, never have had disease's from those eggs, some were NPIP, some not....actually it's safer than buying juvenile or full grown birds from a breeder, especially the ones who advertise on Craigslist.