Pay it forward
There are now many companies who are doing what we refer to as "pay it forward". They underbid a job. They actually lose money. But it keeps them going for a few more weeks. To cover themselves they go out and underbid a second job and use the cash from that to finish the first. Then a third to pay the second. But at some point they go
into economic collapse. All their customers from the first to the last suffer. The first customers who got a great deal have no one to cover the warranty. The last customers paid and in some cases get little or nothing for their money. Avoid companies that are underbidding the job or who have been in business two years or less.
Out of Town
If the people are from out of town they won't be around to cover the repairs and warranty.
If they don't have a license sooner or later they will get caught or leave town. This leaves you with a job half finished or without warranty.
Be very careful that the person who is doing the work is actually the one with the license. A common (and illegal) practice has been for people do do work under someone else's license. This gives you (the homeowner) a false sense of security. Unfortunately this can also result in permits being denied or the finished work being torn out and having to be done because
the county will not approve it.
If they do not have insurance and someone gets hurt on the job "you" could be stuck paying medical bills and even their loss of wages.
Hire a qualified professional who offers you a reasonable deal, but who does not offer a bid that is "too good to be true"