For any Marketplace platform to function & grow well both sides of the user base needs to be developed in tandem. Initially depending on the service the Marketplace is trying to provide, it is important to focus on users that will provide the service.
Uber: Drivers, Clarity: Experts, eBay: Sellers, UpCounsel: Lawyers etc. At the same time these service providers need optimum infrastructure, tools etc to showcase their services in order to attract consumers. Once you have a good number of service providers, you should begin promoting & targeting consumers. Without consumers the two-sided marketplace will not function.
Though you can begin focusing on the consumers later, it might make sense to begin targeting a small sample of users so they serve as initial users/beta testers of your two-sided marketplace.
Hope this helps. Happy to connect further over a call to get into specific strategies.
I've done this before and the answer is tricky: you do both at the same time. It's essentially a conundrum, right? What came first the chicken or the egg?
I can help you organize your thoughts and give you actionable items to complete so you can attract and acquire both types of users/customers at the same time. The key to it is collecting customer information before your product/service even exists.
I can coach you through the process, tell you exactly how to execute, and what tools to do it with.
If our call isn't effective and you don't think I helped, I will refund your money. I'm harder on myself that you will be, so I'll refund your money if I don't think I helped you much.
I have worked at a large marketplace company for over 7 years. The general answer to this is to find service providers (or "experts" in clarity speak) first, and then go after the buyers.
1. Getting providers is cheaper than finding buyers
2. Buyers won't come to your site without an "inventory" of providers
3. Providers create SEO karma
4. You will figure out the issues with your idea or service as soon as you start talking to providers.
Of course, the specific answer depends on your business idea.