What are great examples of successfully launching digital two sided marketplaces other than the Airbnb example people always quote?

I've been developing web and iPhone apps for a while and I usually recommend to first use the provided sharing mechanisms. They provide great flexibility and as well don't require your app to request permissions on external networks. Using the iOS SDK sharing components will also save you precious development time. The most important part is the content that will be shared. On that side, make sure all the content has a unique URL, and can be properly consumed on all plateforms, desktop and mobile. Pay a particular attention to the head meta tags of those pages. Open graph and Twitter tags are not optional anymore and help driver a better visibility on the networks your content is being shared onto. Don't forget to track with an appropriate analytics tool how your users use the sharing module. Then you can evaluate the pertinence of building something custom.

I provide conversion optimisation services on a price per day on a rolling monthly basis. I did it this way, because my background is in software development consultancy and everything was estimated and billed out on a daily basis. I also provide one off services which is normally priced based on how long it would take to complete. I prefer to work with customers on a rolling monthly basis because I can have an impact on many aspects of their digital marketing and business processes. It means I'm also not tied to only creating split tests but have the freedom to advise and have a positive impact on multiple areas of a business.

I don't even know how to answer this. Do you know what the difference between McDonalds and the local burger joint that is filing for bankruptcy is? It's marketing. McDonalds is worth billions of dollars not because of the quality of their food, but because of their marketing. Marketing is not an expense. A janitor is an expense. Your computer is an expense. Marketing is an INVESTMENT. Would you shop around for the cheapest heart surgeon? Of course not. Because you would likely end up dead. Why, then, do you shop around for a marketing expert? Are you ok with your company going bankrupt? Is that worth the small savings to you? No. Of course not. Hire someone who is good at marketing. Hire someone who knows what they are doing. Buy yourself a Lamborghini with your profit the first quarter. Get a beach house in hawaii. Grab a yacht. Or, try to find your business the cheapest heart surgeon you can and then spend the next five years wondering why such a solid business idea failed in the first 6 months. I'm passionate about this exact topic because all those statistics you read about "70% of businesses failing in two years" are solely because of horrible marketing.

The best way to work around something like this is to map out the long-term strategy in phases. Build out a brief project map that outlines what they will receive within the 1-3 month period, the 4-7 month and the 8-12 month period. Set micro objectives for each period and this will give the client a bit more confidence in the short-term plans as well as the long. The key thing to remember here is that the client will often be worried about being tied into a contract that doesn't deliver results. As a result, you need to show why you need the time that you do. One thing that I often throw in is an extra incentive for longer contract lengths - for example, an extra PR/content campaign or some paid advertising extras. Try to assure them of some shorter term results that you can obtain as 'quick wins' and build their confidence this way - the major targets will always be longer term but if you can demonstrate that there will be progress between then they will be a lot more receptive.

Remember when you start a business or are an established business you have to decide who is your perfect customer, since not all potential customers are equal, and not all potential customers are profitable. It is likely that the type of customer who is purely price orientated like those on Elance etc. may not be profitable to your overall business success as it is very unlikely they will pay you more in the future. You would be better focusing your marketing attempts on finding customers who do appraciate your work and understand the added value your agency has to offer, than chasing jobs, by people that only value you and your business by lowest price, which is a business model that can only lead to failure.