When I lived in Mexico for two years (as a young woman) and would have chili in a restaurant I would always check for TWO things:
1. If the chili BURNS my lips, then there is NO WAY that it will be allowed to burn my insides.
2. Check the bowls of salsa: if it's too hot for the flies to land on, then my tummy won't like it either.
BTW: Mexicans lead the WORLD in stomach disorders. Are we surprised? Not me.
They use spices to kill off stuff that is worse, in the food itself.