Eating the animals slaughtered by a person of an unknown religion

Q 3: What is the ruling on eating the meat of an animal slaughtered by a person we are not sure about the soundness of their `Aqidah (creed)? Nowadays truth is mingled with falsehood! Many people commit Shirk (associating others with Allah in His Divinity or worship) and Kufr (disbelief) when they abandon Prayer (Salah), slaughter or make vows to people other than Allah, mock at and oppose true Muslims who abide by Shari`ah (Islamic law), deride the laws of Allah, swear at their destiny, give preference to their wealth, titles, and clothing over offering `Ibadah (worship) to Allah, insult Din (religion) etc. Animals are slaughtered in a big slaughterhouse where slaughtering is done manually not by electric machines. Nevertheless, we do not know the condition of the butcher who does the slaughtering because the latter sells the meat to other butchers who have shops where we buy the meat from. Thus, people who do the slaughtering may be Muslims or not i.e. they may be committing Shirk or Kufr while we do not know as we are ignorant of their personality and `Aqidah; what do we do then? Should we eat from such meat or abandon it as to avoid doubtful matters? It may be worth mentioning that this is nearly the only way through which animals are slaughtered in our country. However, if an animal is slaughtered by a specific person who is apparently Muslim that performs Salah, we do not see them slaughtering or making any vows to anyone other than Allah, no sign of Shirk is seen on them, and they do not insult Din; will it be permissible for us to eat from the meat of such animals as long as we do not see any sign of Kufr on the slaughterer or do we have to verify the soundness of their practice of Din before we eat from the animals which are slaughtered by them?