I am a professional photographer and I get at least 5 opportunities a week from Thumbtack. Most of the 'first' names of the people seeking a photographer are unpronounceable which lends me to think that a lot of this is fake because when I do submit a bid, I never hear back from anyone.
I even tried to underbid by low balling my fees and still do not hear from anyone, yet Thumbtack wants me to spend more money for credits.
Overall, I think Thumbtack provides a lot of fake customer names and just takes money for credits. In better words...no jobs.