But current is always best, this way you might be able to see a job in progress and speak to his current customers about how the job is being handled. If its going well they will be glad to answer your questions. That's why you have specialty trades. So before the job starts always obtain a certificate of insurance. This will tell you what they are insured for and for how much.
Many contractors advertise that they are insured but for what.
It is not required that you put anything down. That is only standard by industry as a sign of good faith. You will find many contractors, that wont ask for a penny up front. The answer is False. To kill the myth about a contractor with complaints and how you shouldn't hire them is this.