“Health & Wellness” by Ann Lukits. The Wall Street Journal, 7/14/2015.
As expected, many people get sick from eating wild mushrooms, but surprisingly, rarely because of eating a poisonous variety, toadstools we call them. Only 1% of the 10,000 mushroom species are poisonous. In a European study, 87.7% of the illnesses came not from eating a poisonous species, but from toxic microorganisms that can grow on any mushroom if they are not cleaned and stored properly. (In my area, commercial mushrooms are grown on horse manure.)
Do not eat any food that squeaks when you bite into it is my recommendation. That simple rule will avoid any mushroom risk. The squeak is the vegetable screaming out in pain, and they will get you back once inside your stomach.