In my country (in the West) there are a few brand of halal food. Most of them use electronarcosis before slaughtering the food. In theory, the brands say the animal is still alive when they slaughter it, but in practice some of them may have died due to the shock.
Some brand use strong electronarcosis, some use light electronarcosis which reduce the risks (but still the consumer can't be sure at 100% the animal wasn't dead before the slaughter).
Can we eat from these brand ? In this industrialized society we can never be 100% sure the meat is halal since we were not in the slaughter house. Therefore, is confidence enough or no ?

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If you know that animal was stunned to death then you cannot eat it.

Confidence is only if a Muslim tells you it is halal then you can trust their word.