Let me go through the process as I see if from a recent computer help needed...
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5 people buy X# of Quotes to bid. (Cost the bidder $$)
Sometimes, not all quotes are looked at and Thumbtack says they refund the # of quote credits if the quote is not looked at, but lets get real... 5 Quotes get looked at, because that's what the customer will do... 1 bid is accepted... Profit for Thumbtack is 4 quotes based upon the non-wining bids, + 1 quote for the one that did win the bid... This sums up the amount you can lose if you don't win bids because you refuse to under price your services to win bids. It'd be cheaper for me to advertise in free places/spaces and pick the work I'll do. As a side note the 1st time I used it was a free try and someone needed a power supply for her laptop. Located one by phone at a nearby BestBuy and told her that was the fastest place to get one for cheap. Another happy customer. Didn't charge her one penny, didn't seem right.