There are essentially no general hard and fast rules like that when it comes to mushroom hunting, there is no substitute for knowing how to positively identify specific species, where specific species should be growing, and knowing what distinguishes them from similar poisonous species.
I don't see why this could possibly get downvoted, it's absolutely true. If you do have a "hard and fast" rule in mind, it may work in your region but not in other places.
> If you do have a "hard and fast" rule in mind, it may work in your region but not in other places.
There are lots of hard and fast rules in different regions though that do work if you can ID the mushroom to genus. E.g. in New England, no green mushrooms in the Russula genus are poisonous.
