The posuk states “Tamim Tihiyeh Im Hashem Elokecha”(Devarim 18:13)
There is a famous story told about The Chofetz Chaim
A few boys from the Yeshiva came to complain to the Chofetz Chaim. They had given someone money in a business venture and the man cheated them and stole all their money.
The Chofetz Chaim said I understand your problem and where you went wrong. Since you are innocent Yeshiva boys and you are accustomed to trusting in Hashem with purity and wholehearted faith. You carried over that attitude to your dealings with this businessman and his grand scheme. But the truth is, if you read the posuk it says clearly, “Tamim TihiyehIm Hashem Elokecha”, go innocently with Hashem…
You can only be trusting when Hashem is your partner, but when you give your money to people you must be wary and not be gullible.