If you think that it is not necessary to talk to previous clients, think again. If you think that you are making the contractor uncomfortable, don’t.
Most of the time you can get away with one question – would you hire this contractor again?
Construction is not a one day project, issues come up all the time. Had your contractor worked hard to fix the issue?
Bonus questions: Have you managed to stay on budget? On schedule?
Golden question: what would you do differently if you were to do it all over again. All you need to do is listen.