Can an effective online marketplaces for leads and referrals exist?

I have been evaluating a number of online marketplaces for sales leads and business referrals.  It seems that a qualified lead constitutes many different things to different people, making it extremely challenging to automate this type marketplace.  

As a rollup of a cottage industry, I get it. As a way of lovering cost per acquired lead, I get it. As a way to transform selling for the high volume low value add cold calling, I get it.  Just not sure if it can be done effectively online.