Question:
What is the definition of someone who is "muchzak b'kashrus" who can be relied on regarding kashrus even though he is making money from the food's sale?
Answer:
To be considered a “muchzak bkashrus” (Rema Y:D 119-1) the Aruch Hashulchan 119-11 says that the person has to be known to be an upstanding religious Jew. He daven three times a day, puts on a tallis and teffilin in the morning, washes his hands to eat, keeps a kosher home etc. This is to fulfill what the Rema says, however, nowadays based on the Taz Y:D 119-1 that due “kilkul hadoros”, therefore there was a takana called “takanas Haaratzos” that we should not buy something even from someone who is muchzak b’kashrus unless he has a hechsher from a Rov.
Sources:
Bais Hillel Y:D end of siman 55, brought in Be’er Heitiv Mahari Tiktin 119-3, Darcei Teshuva 119-6.