Good reference check questions on behalf of a general contractor?

[Bruce P.]

Hi BP,

My friend is trying to make a decision around hiring a general contractor and is getting ready to start vetting the contractor's references. Here are some questions I suggested they ask - are there any others you would ask? Specifically they are building an ADU in southern California LA area if that makes a difference.

• Can you tell me about the work performed?
  How do you know the contractor?
  Did you encounter additional costs outside of your original quote and were you okay with how they were handled?
  Were you able to communicate effectively with the contractor?
  Are you happy with the final result and would you hire them again?
  Did the project fall within the allotted timeline? Why or why not?
  Was the job site kept clean and safe?
  What type of warranty were you provided with and have you had to use it?
  Were subcontractors used and were you happy with their work?
  Did you check the contractor’s credentials?