You'll need to open up all the cupboards and look for any signs or staining or discoloration that would indicate water leaks. Also, around each window, any "dimpling" or anything that looks like raised wall-paper. Look out for floors that are soft or have any kind of "give" Step everywhere on the floor and look for signs of this!
On the outside, also look for any kind of "rippling" in the finish, or spots that don't seem right to you,
Ask how often they caulked the roof. Any answer that is less than twice a year should be a tip off.
Hope this helps,
WoodGlue