Interesting project. There are a few points which come to mind. Seen this type of business on the web & think that there is one major point in that the 'expert' appointed must be a true 'expert' in the field . For example, a Lawyer asked a technical issue of law in the Country you reside in must be able to fully understand your question & the 'background ' of the question. It is very difficult to satisfy someone via a short 'conversation' or text if the subset of the question is not in the area of expertize.
A second point is how can you be satisfied with your 'experts' unless there is a considerable amount of vetting & monitoring. All this takes time & who pays for that time. A busy 'expert' in their own profession would not be interested, yet the is the type of person you want. Someone with time on their hands may not be a worthwhile expert.
This is the reason we're not building marketplace but want to integrate with other marketplaces. We believe one team cannot focus on evaluating every business out there and create good software the same time. Some company will have 'doctors' other will have lawyers etc.
Ofc there's also an option to use without any marketplace - just share your profile on your blog/website etc.
Regarding second point - there're 2 answers:
1. Simply busy expert can charge more :-) There's a saying that everyone has his price - $1000 / minute and you have incentive (ofc I don't think many people will charge this much - but we left the space open as well for celebrities - not only consultations)
2. Busy people often need to filter out their clients and this is perfect tool to do so. We've already made few partnerships and this is especially the case where companies see the potential (MME and BitcoinSuisse)
Thanks for the answers. Guess I was stating the obvious, but have used web based advice previous & found it somewhat lacking. Look to see you 'covering all bases'.