Having been one of the people who built Thumbtack (and a shareholder), this would have been much more of a concern 2 or 3 years ago. At this point Thumbtack (and other companies like Homejoy) are big enough to be able to compete against huge companies.

It isn't like the big guys can just jump into the market and undercut everybody on price. Most people who hire service professionals are looking for a high quality experience at a good value. Actually finding those high quality professionals and facilitating the experience with a customer is really really hard. You can't just underprice everybody, you can't just find the cheapest service providers.

And having previously worked at Google, local services is like 10x higher touch than any other business Google has. Maybe they bite the bullet and try to do it, but this isn't a very Google-like business.