You can ask if he knows how to tell time…
Or if he minds a jab in the ribs if he goes to long…
Will he kick you out if you talk during davening…
Does he minds not having aminyan till 10 on shabbos morning
And if course will he let you be mechalel shabbos by using the eiruv…
This is all in Flatbush. Everywhere else you should prob check with his rebbeim