For two sided marketplaces, I recommend having strategies for the following areas:
1) Strategies for solving the chicken-and-egg problem in the beginning, as many multi-sided marketplaces fail to gain traction due to this problem. Buyers need sellers in order to show interest; sellers need buyer in order to come. Some strategies to solve the chicken-and-egg problem:
a) Determine which side "makes or breaks" your business, and find key initial anchor tenants on that side. Usually, it's the buyers, as sellers will go where there's demand. Pay/give incentives to those initial anchor tenants if you have to.
b) Keep it to an initial segment or two in order to establish critical mass. Don't be all over the place. Establish a niche first where your buyers and sellers can meet.
c) Fake it till you make it. The founders can pretend to be buyer/or seller in the beginning. Also make some convincing "fake" profiles so that the marketplace does not look to empty.

2) Strategies that create and maintain high value-add interactions between all sides in the marketplace. The marketplace needs to help buyers and sellers capture consistent value effectively and efficiently. Once you solve the chicken-and-egg problem, you need your users to stick. Some strategies:
a) Create a reputation system to ensure quality buyer and seller interactions.
b) Give your sellers adequate tools for creating products and services.
c) Optimize how your buyers can best search and filter the products, services, and sellers they need.
d) Be very clear how buyers and sellers can transact for goods and services. Make the process simple and easy to follow.