Check the references the trade professional provides you with, they are always a good indicator about what you can expect from the trade professional.
The Thai Do It reference model is also a good way to learn more about the trade professional. Many principals record - upon completion of a Thai Do It job a reference for the benefit of other principals. They are able to enter a motivation for their rating.
When you need to have a big job done, it sure pays to visit one or two of the jobs that have been given as a reference. That way you will have a crystal clear idea about the trades person you would like to use.