Disclaimer: I haven't checked out your site. Response is based off what you wrote.

To start thumbtack is a free service to customers providing gigs. Contractors must pay to place bids.

Clarity is free for consultants/experts and customers pay.

There are issues with both:
TT: Because is free for 'giggers' they often don't think through what they are asking for and how willing they are pay. This causes contractors to have high expenses here. They even mention that it takes 10bids to get one client.. That's about $100 spent first. They have users because is free for giggers and where there's a demand there will be a supply. I personally think that if they improved their contractor side to be cheaper or more flexible in what is expensed they would have more contractors bidding. They attracted the demand first- find contractors and have them bid or you helping you get better pricing, for free.

Clarity, I'm not sure how it stated getting traffic, I think it was through getting 'experts' first. I for example signed up early on and let my account kind of just sit there until i later became more engaged. The demand however is gained through paying customers but their funnel system is designed so that people come here for Q&A and leave it to us to sell ourself and thus get their revenue... A while back I helped curate an idea from Clarity that, although I never got follow up on my consultation, led to the now offering of videos on demand. These videos help in that transition from a call or answe to now paying for a video.
My personal opinion that is a bit of a problem for us as consultants- is that experts aren't really curated as much. This dilutes the possibility of some being able to make decent income continuously rather than as a weekend money resource or marketing for our actual businesses. If Clarity curated more I think the quality of answers would go up, paid calls would increase, and definitely some 'experts' would be vetted out, maybe even myself. I'm an MBA, serial entrepreneur, current business owner, previous small cap investor, marketer, web developer and sometimes i see answers that just surprise me! Some do state they provide opinions and some give hard advice but their advice is wrong, worst thing is that they have more calls than a lot of us. So whatever they do it works for them, and great for them, but again the vetting is an issue. For clarity users this in it self is not a problem beucause they may get their motivation up or get more guidance than what they currently have, even if is not the most accurate, because of this the level of 'expertise' is not an obvious problem.

(( If your an expert i don't intend this to be a rude assessment of your services or a blanket statement, I pointed that out just not to ignore that fact. ))

If you grow a consulting or crowd sourcing service you need to ensure quality quality from the ground up. Quality helps overcome the trust hurtle, make sure that your first chefs are amazingly friendly, qualified and available to your other market. For leads you might feel like your dealing with the chicken or the egg, right? But the truth is that you can build both sides through dedicated marketing. As you expose your general branded service people from both ends will see their own value (if they are in the current situation and thus recognize the market need or opportunity) and become your users.

Bootstrap it: visit chefs and introduce yourself and your business. Find chef bloggers in your market, find pull marketing partners- third party business that might benefit from their own chefs exposure through ok your site and thus they they do the pulling of chefs for you.

I hope this helps at least a bit! Be creative, have fun and get some users!

Humberto Valle