Here are the ones I asked to get the real scoop on personality/midos (during the years I helped people with shidduchim).
1.Have you seen the boy in a situation where he could have been JUSTIFIABLY upset or frustrated? How did he handle it?
2.If you had to describe him in 3 or 4 adjectives,which would you use?(then compare what other references used)
3.For learners:you must speak to chavrusos and roommmates.In the Bais Medrash alone, everyone is either “geshmak” or “aidel”.Or “mamesh a mushlum”(completely perfect midos).
Hope this helps a little.