Hi
There would be 2 different types of business. In the marketplace you have to get both the users and the payer so you have to have 2 set of tactics. Some of them are:
1. creating your own supply (for some time you work as the supplier) i.e. Uber hired guys, Udemy produc coures on its own
2. you try to satify as well as possible at least one part of the marketplace - Udemy concentrated on the professors
3. convince suppliers to bring their own customers - again Udemy
4. use other platform. Airbnb use craiglist Udemy used Groupon
5. create enough liquidity so that
6. upsell to the customers
7. make refferal program - have a look at dropbox case.
here ther is a lin to the Udemy creator talkin about marketplaces and a nice presentation as well. The presentation and the movie is in English; the rest in Polish but please do not pay attention to it:
http://startupakademia.pl/2015/02/04/jak-stworzyc-marketplace/
Subsription model - well it is just the ecommerce but with different payment: so direct, earned, paid traffic; lots of affiliate. Some tricks are: preinstalation, different payment plans, refferals etc
Have a nice day
