If you’re satisfied with the contractors’ legal requirements, move on to the next important steps, their reputation! What do others, who have worked with your potential contractor in the past have to say about her/his work? How they leave a past client is a telling factor on how they will treat you. It is important to also be forming your own opinions, however, it is better to be safe than sorry. You can also check with the Better Business Bureau and look up reviews that have been written before or simply ask for references.
Asking to see past work, or to speak with past clients is not a strange request, especially if you’re going with a relatively new contractor.