Yeah, I too have had similar issues like JRA. I payed for a lead, I think $8, and never heard back from the client, so I tried to get a refund and never heard back from thumbtack either. Also, I've noticed since I'm on the free version that each lead cost increases, it started out free, then was a few dollars then $8, now I think its up to $12 or so. But most weddings have been the entire farm for under $1k. So I don't even bother.
On the other hand, it could be better than advertising with the Knot or Wedding Wire. I'm currently trying to decide where/if to advertise but WW is $4k a year for premium placement. I figure that most brides probably only skim the first few pages, like Google, so going with anything other than their top placement would be a potential waste of money. But I don't have $4k to spend on advertising yet...