Bismillah al-Rahmaan al-Raheem
Firstly,let me give the general and basic ruling regarding halal meat: For meat to be halal, it must be slaughtered according to Islamic laws. The conditions for slaughtering an animal in the Islamic way are as follows:
- The person slaughtering must be a Muslim
- He/she must make the intention to slaughter and utter the name of Allah before slaughtering
- The animal must be facing the Qiblah (It is also recommended that the person faces the Qiblah)
- The tool for slaughtering must be made of iron
- The animal should show some movement after being slaughtered; at least it should move its eyes or tail or strike its foot on the ground. This law applies only when it is doubtful whether or not the animal was alive at the time of being slaughtered, otherwise it is not essential.
- It is necessary that the blood should flow in normal quantity from the slaughtered animal.
Now, with regards to the questions:
1) One of the conditions is that the animal must be alive before the slaughtering. Therefore, if stunning the animal results in its death, then it does not fulfill one of the conditions and thus is haram to eat.
However, in a slaughter-house:
- If you have a doubt whether some animals have died or not (in the case that stunning leads to unconsciousness), then it is halal to eat from it.
- If you have certainty that some of them die, and if the number of animals that die due to stunning is very minimal, but it is not known which ones, then:
- If it is within a small limited number of slaughtered animals, it is haram to eat from any of them.
- If it is among a very large number of slaughtered animals, it is halal to eat from them.
2) If a Muslim owner says that the meat he is serving is halal, then it is fine to eat from there (unless of course you are already certain that he is lying or has made a mistake. But investigation is not required!).
However, if the owner is a non-Muslim, then it must be investigated.
The above are the rulings regarding your question. When it comes to implementing the ruling, it is a personal responsibility to judge our case based on the rulings presented to us, and apply these with sincerity and Taqwa.
May Allah give all of us the tawfiq to only eat from what is halal