Agaricus could be confused with white amanitas if they miss the capsule or the annulus (capsule is the biggest danger sign). Or a parasol with a A. pantherina. TBH, even the distinct Coprinus comatus could be confused by a beginner to another ink cap that could be really nasty if eaten with alcohol. I guess mushroom hunting requires a lot of common sense, perception and experience, which a lot of people lacks to some degree.