1. Like an ethical dog breeder, a good contractor has a waitlist

Quality contractors are booked.  Immediate availability is a red flag.  If you need someone to begin next week, you will mostly attract shady or new firms.

Major red flag: most companies you contacted had a waitlist.  Finally, you found one who can start next week.  He may also apply more pressure on you and make more follow-up calls.  So look for any sign of desperation.

9. While prices will vary sometimes considerable, the lowest bidder is a red flag holder