Check out SuperFastYellowPages.com. Vendors only pay a flat fee of $10/month per zip code for unlimited leads and bids.
On Thumbtack vendors have no way of verifying that the leads are legit. Just like on Google AdWords advertisers have no way of verifying that their clicks are legit.
Google is an investor in Thumbtack and it appears to me that both business models are not beneficial to small business owners at all. It's time for a new business model that creates a level playing field for all and doesn't hurt the small business owners with shady and unethical tactics.
Product or Service Mentioned: Thumbtack Leads.