A kosher concern

Q: How should one act in a house in which there is a concern that the food is not kosher because the family is not observant but they say that they keep kosher?
A: It is impossible to rely on them for two reasons:
1. Perhaps there are halachot of which they are unaware.
2. Perhaps there are halachot of which they heard but they think they are stringencies.
It is possible that it is 100% kosher, but you cannot be certain.
There are therefore a few options: You can do your homework and gently check with them or you can act like Ha-Rav Eliyahu Lapian (brought in "Lev Eliyahu" vol. 1, p. 18 in the introduction) in which he was invited to eat a few times and he did not want to embarrass the one inviting him, he therefore said that the doctor forbade him from eating the particular food. And he explained to his students with a smile that he was not lying, G-d forbid, since the Rambam was a doctor! There are also many doctors in the State of Israel who say that there are all sorts of problems of overeating.