‏السلام عليكم ورحمة الله وبركاته أحسن الله إليك Sheikh what are the things to ask for while doing istifsar for potential wife? In my culture it is very common to look into previous bad habits/sins of the potential spouse. ‏جزاك الله خير

Ask about the religion and the manners, because that is what you will actually live with. Be normal about it. Ask about education, work, how free time is spent, who the person takes knowledge from, and let the akhlaq show itself in the conversation. Present defects and a buried past are not the same thing. Imam Ibn Baz said that neither side may conceal defects and that clarifying them is obligatory, so whatever is still the case must be answered honestly, and if you are the one being asked, describe your present state truthfully. As for a sin that Allah has concealed and the person has repented from, the other side is not entitled to it, and the scholars state that a person should not go and inform a future spouse of what Allah has covered for him.