This is my very first BLOW so please bare with me.  My newly renovation on my master bath came to mind right away. 
I have been in Real Estate for the past 28 years, so it is a little embarrassing for me to tell this story.  But, I do so as a lesson to others so that no one else has to go thru the problems we had.
We were using natural stone so I knew that if the tile work was not really good I would not be at all happy.  I went to a well known tile store to look for tile and they were remodeling their whole store.  I waited until their work was done and was impressed with all the displays and workmanship.  I met the young man who did the remodeling and asked him to look at my job and give me a bid.  I was also having granite replaced in my kitchen and new appliances.
He said that he could do both jobs and gave us an acceptable bid.  In the contract we signed, he gave his contractor's license number.  I felt all was in order.
The first day they demolished my old bath and hauled it away.  The second day, I came home and they had done some framing and I noticed that they had cut holes in my structural trusses.  I said where are your permits.  I was told that he was not going to get permits.  I said "Oh yes you are".  My husband went over to the county to pull permits for the work to be done and found out what the county specs were for the job.  He also found out that our contractor did not have approval for doing the kind of work we had contracted for and was not qualified to do a job as extensive and expensive as ours.
We dismissed this contractor and had to find others to come and remedy the mistakes he had made and do it right.  It was quite expensive in time and money.
I learned that it is not enough to know a contractor is licensed, but to know what kind of license and what kind of work that license permitts them to do.  Take heed.