what is the reason that in the case of Achan they were punished? The Gemara answers: Achan’s offense was not a hidden matter because his wife and children knew about it, and they did not protest. § When God explained to Joshua the reason for the Jewish people’s defeat at the city of Ai, He said: “Israel has sinned” (Joshua 7:11).

(20) Achan answered Joshua, “It is true, I have sinned against the LORD, the God of Israel. This is what I did: (21) I saw among the spoil a fine Shinar mantle, two hundred shekels of silver, and a wedge of gold weighing fifty shekels, and I coveted them and took them. They are buried in the ground in my tent, with the silver under it.” (22) Joshua sent messengers, who hurried to the tent; and there it was, buried in his tent, with the silver underneath.

(10) A male or female convert who [was already a part of the community] comes and says, “I was appropriately converted by a beit din of So-and-So," they still should not be believed to come to the congregation [get married] until the witnesses [of the beit din] come. But if you see them behaving in customs worthy in the way of Israel and they do all of the mitzvot, they are presumed to be righteous converts, in spite of the fact that there were no witnesses to bear witness about who converted them.